[Moto G7 Power ROMs, Kernels, Recoveries, & Other D] ViRUS2015:
Nope, in my case I had the phone fully stock before trying this. I did the whole preparation first anyway, removed my Google Account from the device and factory reset it, then flashed the downloaded factory firmware image as instructed in step 04 with the console commands in dogbin.

I'm using TWRP-ocean-test-1 from the thread OP linked. I can't use the exact one posted by the OP in that other thread since for some reason the touchscreen doesn't work with it.

By the way, how did you end up in slot_b on TWRP? Unless I'm missing something, in no step the OP says to change to that slot during the preparation or installation steps :/

--------------

Also, I just tried starting everything from scratch. Before going to bed last night, I reflashed the original factory image I downloaded from lolinet only to install WhatsApp and use the alarm. This morning, I re-did everything carefully and got logs at every stage, here they are:

Stage 1: These are steps 4 and 5 of the preparation. I removed my Google Account and factory reset the device, then I rebooted into fastboot and began entering the commands from the dogbin page. As far as I can tell, the console shows no errors at this stage.

Microsoft Windows [Versión 10.0.18362.356]
(c) 2019 Microsoft Corporation. Todos los derechos reservados.

C:\Windows\system32>cd G:\Cosas\Android

C:\Windows\system32>G:

G:\Cosas\Android>fastboot set_active a
Setting current slot to 'a' (bootloader) Slot already set active
OKAY [ 0.001s]
Finished. Total time: 0.004s

G:\Cosas\Android>fastboot reboot-bootloader
Rebooting into bootloader OKAY [ 0.000s]
Finished. Total time: 0.001s

G:\Cosas\Android>fastboot getvar max-sparse-size
max-sparse-size: 268435456
Finished. Total time: 0.000s

G:\Cosas\Android>fastboot oem fb_mode_set
OKAY [ 0.003s]
Finished. Total time: 0.005s

G:\Cosas\Android>fastboot flash partition gpt.bin
(bootloader) is-logical:partition: not found
Sending 'partition' (45 KB) OKAY [ 0.169s]
Writing 'partition' (bootloader) Validating 'gpt.default.xml'
(bootloader) Committing 'gpt.default.xml'
(bootloader) - flashing 'gpt_main0.bin' to 'partition:0'
(bootloader) Flashing primary GPT image...
(bootloader) Flashing backup GPT image...
OKAY [ 0.084s]
Finished. Total time: 0.260s

G:\Cosas\Android>fastboot flash bootloader bootloader.img
(bootloader) is-logical:bootloader: not found
Sending 'bootloader' (7419 KB) OKAY [ 0.340s]
Writing 'bootloader' (bootloader) Validating 'bootloader.default.xml'
(bootloader) Committing 'bootloader.default.xml'
(bootloader) - flashing 'emmc_appsboot.mbn' to 'aboot'
(bootloader) - flashing 'rpm.mbn' to 'rpm'
(bootloader) - flashing 'tz.mbn' to 'tz'
(bootloader) - flashing 'devcfg.mbn' to 'devcfg'
(bootloader) - flashing 'cmnlib_30.mbn' to 'cmnlib'
(bootloader) - flashing 'cmnlib64_30.mbn' to 'cmnlib64'
(bootloader) - flashing 'keymaster64.mbn' to 'keymaster'
(bootloader) - flashing 'prov.mbn' to 'prov'
(bootloader) - flashing 'sbl1.mbn' to 'sbl1'
OKAY [ 0.324s]
Finished. Total time: 0.678s

G:\Cosas\Android>fastboot reboot-bootloader
Rebooting into bootloader OKAY [ 0.001s]
Finished. Total time: 0.002s

G:\Cosas\Android>fastboot flash modem_a NON-HLOS.bin
(bootloader) is-logical:modem_a: not found
Sending 'modem_a' (65396 KB) OKAY [ 1.585s]
Writing 'modem_a' OKAY [ 0.505s]
Finished. Total time: 2.125s

G:\Cosas\Android>fastboot flash fsg_a fsg.mbn
(bootloader) is-logical:fsg_a: not found
Sending 'fsg_a' (11684 KB) OKAY [ 0.421s]
Writing 'fsg_a' OKAY [ 0.092s]
Finished. Total time: 0.533s

G:\Cosas\Android>fastboot flash dsp_a adspso.bin
(bootloader) is-logical:dsp_a: not found
Sending 'dsp_a' (16384 KB) OKAY [ 0.521s]
Writing 'dsp_a' OKAY [ 0.105s]
Finished. Total time: 0.648s

G:\Cosas\Android>fastboot flash logo_a logo.bin
(bootloader) is-logical:logo_a: not found
Sending 'logo_a' (1285 KB) OKAY [ 0.196s]
Writing 'logo_a' OKAY [ 0.045s]
Finished. Total time: 0.251s

G:\Cosas\Android>fastboot flash boot_a boot.img
(bootloader) is-logical:boot_a: not found
Sending 'boot_a' (32768 KB) OKAY [ 0.937s]
Writing 'boot_a' (bootloader) Image signed with key bad key
OKAY [ 0.633s]
Finished. Total time: 1.604s

G:\Cosas\Android>fastboot flash dtbo_a dtbo.img
(bootloader) is-logical:dtbo_a: not found
Sending 'dtbo_a' (1760 KB) OKAY [ 0.206s]
Writing 'dtbo_a' OKAY [ 0.043s]
Finished. Total time: 0.258s

G:\Cosas\Android>fastboot flash vendor_a vendor.img_sparsechunk.0
(bootloader) is-logical:vendor_a: not found
Sending 'vendor_a' (259120 KB) OKAY [ 5.780s]
Writing 'vendor_a' OKAY [ 1.368s]
Finished. Total time: 7.261s

G:\Cosas\Android>fastboot flash vendor_a vendor.img_sparsechunk.1
(bootloader) is-logical:vendor_a: not found
Sending 'vendor_a' (147628 KB) OKAY [ 3.359s]
Writing 'vendor_a' OKAY [ 0.685s]
Finished. Total time: 4.112s

G:\Cosas\Android>fastboot flash vendor_b vendor.img_sparsechunk.0
(bootloader) is-logical:vendor_b: not found
Sending 'vendor_b' (259120 KB) OKAY [ 5.775s]
Writing 'vendor_b' OKAY [ 1.365s]
Finished. Total time: 7.253s

G:\Cosas\Android>fastboot flash vendor_b vendor.img_sparsechunk.1
(bootloader) is-logical:vendor_b: not found
Sending 'vendor_b' (147628 KB) OKAY [ 3.362s]
Writing 'vendor_b' OKAY [ 0.689s]
Finished. Total time: 4.119s

G:\Cosas\Android>fastboot flash oem_a oem.img
(bootloader) is-logical:oem_a: not found
Sending 'oem_a' (103016 KB) OKAY [ 2.402s]
Writing 'oem_a' OKAY [ 0.507s]
Finished. Total time: 2.962s

G:\Cosas\Android>fastboot flash oem_b oem.img
(bootloader) is-logical:oem_b: not found
Sending 'oem_b' (103016 KB) OKAY [ 2.407s]
Writing 'oem_b' OKAY [ 0.523s]
Finished. Total time: 2.981s

G:\Cosas\Android>fastboot oem fb_mode_clear
OKAY [ 0.002s]
Finished. Total time: 0.003s

G:\Cosas\Android>fastboot reboot-bootloader
Rebooting into bootloader OKAY [ 0.001s]
Finished. Total time: 0.002s

G:\Cosas\Android>fastboot boot TWRP-ocean-test-1.img
Sending 'boot.img' (27138 KB) OKAY [ 0.579s]
Booting OKAY [ 0.732s]
Finished. Total time: 1.336s

G:\Cosas\Android>

Now I'm in TWRP, instead of using the interface on my phone, I used ADB Shell to flash copypartitions to gather the logs. Here I flash copy-partitions-payton.zip while on Slot_A as instructed (I checked by going to "Reboot" in TWRP, and it says "Current Slot: A" at the bottom, so I know I'm using the correct one). Here's where the first issues appear. I check the log in TWRP and it says at the top in red:

Could not mount /data and unable to find crypto footer.
Failed to mount '/data' (Invalid argument)
Unable to recreate /data/media folder.
Updating partition details...
Failed to mount '/data' (Invalid argument)
Full SELinux support is present.
Unable to mount /data/media/TWRP/.twrps
MTP Enabled

I proceed anyway, and install copy-partitions-payton.zip.

Microsoft Windows [Versión 10.0.18362.356]
(c) 2019 Microsoft Corporation. Todos los derechos reservados.

C:\Windows\system32>cd G:\Cosas\Android

C:\Windows\system32>G:

G:\Cosas\Android>adb shell
ocean:/ # twrp install /external_sd/copy-partitions-payton.zip
Installing zip file '/external_sd/copy-partitions-payton.zip'
Checking for Digest file...

Partition aboot_a
3072+0 records in
3072+0 records out
1572864 bytes transferred in 0.266 secs (5913022 bytes/sec)
Partition cmnlib64_a
2048+0 records in
2048+0 records out
1048576 bytes transferred in 0.071 secs (14768676 bytes/sec)
Partition cmnlib_a
2048+0 records in
2048+0 records out
1048576 bytes transferred in 0.071 secs (14768676 bytes/sec)
Partition devcfg_a
128+0 records in
128+0 records out
65536 bytes transferred in 0.006 secs (10922666 bytes/sec)
Partition dsp_a
32768+0 records in
32768+0 records out
16777216 bytes transferred in 1.135 secs (14781688 bytes/sec)
Partition dtbo_a
16384+0 records in
16384+0 records out
8388608 bytes transferred in 0.531 secs (15797755 bytes/sec)
Partition fsg_a
24576+0 records in
24576+0 records out
12582912 bytes transferred in 0.806 secs (15611553 bytes/sec)
Partition keymaster_a
2048+0 records in
2048+0 records out
1048576 bytes transferred in 0.072 secs (14563555 bytes/sec)
Partition logo_a
32768+0 records in
32768+0 records out
16777216 bytes transferred in 1.053 secs (15932778 bytes/sec)
Partition modem_a
204800+0 records in
204800+0 records out
104857600 bytes transferred in 6.565 secs (15972216 bytes/sec)
Partition prov_a
384+0 records in
384+0 records out
196608 bytes transferred in 0.015 secs (13107200 bytes/sec)
Partition rpm_a
512+0 records in
512+0 records out
262144 bytes transferred in 0.018 secs (14563555 bytes/sec)
Partition sbl1_a
1024+0 records in
1024+0 records out
524288 bytes transferred in 0.040 secs (13107200 bytes/sec)
Partition tz_a
3584+0 records in
3584+0 records out
1835008 bytes transferred in 0.119 secs (15420235 bytes/sec)
Partition vbmeta_a
128+0 records in
128+0 records out
65536 bytes transferred in 0.006 secs (10922666 bytes/sec)

[OK]

Updating partition details...
Failed to mount '/data' (Invalid argument)
Done processing script file
ocean:/ #
G:\Cosas\Android>

Then I go to Reboot > Bootloader in TWRP. I get a warning that no OS is installed, but I swipe to reboot anyway and proceed using the -w command in fastboot.

Microsoft Windows [Versión 10.0.18362.356]
(c) 2019 Microsoft Corporation. Todos los derechos reservados.

C:\Windows\system32>cd G:\Cosas\Android

C:\Windows\system32>G:

G:\Cosas\Android>fastboot -w
Erasing 'userdata' OKAY [ 0.149s]
Erase successful, but not automatically formatting.
File system type raw not supported.
Erasing 'metadata' (bootloader) Permission denied
FAILED (remote: '')
fastboot: error: Command failed

G:\Cosas\Android>

Here I still get some errors about metadata and some permissions denied, maybe some of these errors are the cause of my problems?

In any case, I keep on going and reboot to TWRP again using the Windows console.

Microsoft Windows [Versión 10.0.18362.356]
(c) 2019 Microsoft Corporation. Todos los derechos reservados.

C:\Windows\system32>cd G:\Cosas\Android

C:\Windows\system32>G:

G:\Cosas\Android>fastboot boot TWRP-ocean-test-1.img
Sending 'boot.img' (27138 KB) OKAY [ 0.578s]
Booting OKAY [ 0.731s]
Finished. Total time: 1.335s

G:\Cosas\Android>

Now in TWRP, I proceed to install the ROM zip + TWRP on Ramdisk as instructed in Step 3 of "ROM - Installation". Needless to say, the errors about /data are still present when TWRP boots up.

Could not mount /data and unable to find crypto footer.
Failed to mount '/data' (Invalid argument)
Unable to recreate /data/media folder.
Updating partition details...
Failed to mount '/data' (Invalid argument)
Full SELinux support is present.
Unable to mount /data/media/TWRP/.twrps
MTP Enabled

Microsoft Windows [Versión 10.0.18362.356]
(c) 2019 Microsoft Corporation. Todos los derechos reservados.

C:\Windows\system32>cd G:\Cosas\Android

C:\Windows\system32>G:

G:\Cosas\Android>adb shell
ocean:/ # twrp install /external_sd/lineage-16.0-20190918-UNOFFICIAL-ocean.zip
Installing zip file '/external_sd/lineage-16.0-20190918-UNOFFICIAL-ocean.zip'
Checking for Digest file...
Step 1/2Step 2/2Done processing script file
ocean:/ #

Then I install TWRP to ramdisk going to Advanced > Install Recovery Ramdisk and choosing TWRP-ocean-test-1.img from my microSD card. Now I also get an error regarding /system in TWRP's log.

Unpacking Boot...
Backing up Boot...
Unpacking /external_sd/TWRP-ocean-test-1.img...
Repacking Boot...
[IMAGE FLASH STARTED]
Image to flash: '/tmp/repackorig/new-boot.img'
Calculating restore details...
[IMAGE FLASH COMPLETED]
Updating partition details...
Failed to mount '/data' (Invalid argument)
Failed to mount '/system' (Permission denied)
...done
Backing up Boot...
[IMAGE FLASH STARTED]
Image to flash: '/tmp/repackorig/new-boot.img'
Calculating restore details...
[IMAGE FLASH COMPLETED]
Updating partition details...
Failed to mount '/data' (Invalid argument)
...done

Now I go to Reboot > Recovery in TWRP. I still get a warning saying that no OS is installed, but I reboot anyway and I succesfully get into TWRP again. I try to install OpenGapps but I get an error 70 complaining that there's no enough space in System partition. If I reboot my phone to system, I get into a bootloop on the bootloader unlocked warning.

Thank you in advance to anyone willing to help me out! Surely I'm missing something trivial due to lack of experience. I've flashed many ROMS before, but this is my first time giving it a try since the A/B partition stuff was implemented :silly: