[Moto G Power Guides, News, & Discussion] WoKoschekk:
My phone is a Moto G6+ and it also has a A/B partitioning scheme. I flashed my entire firmware right away and had no problems with it. Here's the output:

### fastboot flash ALL

C:\Program Files (x86)\Minimal ADB and Fastboot>flashfile.bat

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot getvar max-sparse-size
max-sparse-size: 268435456
finished. total time: -0.000s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot oem fb_mode_set
...
OKAY [ 0.000s]
finished. total time: 0.000s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash partition gpt.bin
target reported max download size of 536870912 bytes
sending 'partition' (37 KB)...
OKAY [ 0.000s]
writing 'partition'...
(bootloader) Validating 'gpt.default.xml'
(bootloader) Committing 'gpt.default.xml'
(bootloader) - flashing 'gpt_main0.bin' to 'partition:0'
OKAY [ 0.126s]
finished. total time: 0.126s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash bootloader bootloader.img
target reported max download size of 536870912 bytes
sending 'bootloader' (9520 KB)...
OKAY [ 0.246s]
writing 'bootloader'...
(bootloader) Validating 'bootloader.default.xml'
(bootloader) Committing 'bootloader.default.xml'
(bootloader) - flashing 'xbl.elf' to 'xbl'
(bootloader) - flashing 'prov64.mbn' to 'prov'
(bootloader) - flashing 'cmnlib.mbn' to 'cmnlib'
(bootloader) - flashing 'cmnlib64.mbn' to 'cmnlib64'
(bootloader) - flashing 'abl.elf' to 'abl'
(bootloader) - flashing 'keymaster.mbn' to 'keymaster'
(bootloader) - flashing 'storsec.mbn' to 'storsec'
(bootloader) - flashing 'rpm.mbn' to 'rpm'
(bootloader) - flashing 'pmic.elf' to 'pmic'
(bootloader) - flashing 'hyp.mbn' to 'hyp'
(bootloader) - flashing 'tz.mbn' to 'tz'
(bootloader) - flashing 'devcfg.mbn' to 'devcfg'
OKAY [ 0.201s]
finished. total time: 0.462s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash modem NON-HLOS.bin
target reported max download size of 536870912 bytes
sending 'modem_a' (77976 KB)...
OKAY [ 1.922s]
writing 'modem_a'...
OKAY [ 5.392s]
finished. total time: 7.314s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash fsg fsg.mbn
target reported max download size of 536870912 bytes
sending 'fsg_a' (7412 KB)...
OKAY [ 0.175s]
writing 'fsg_a'...
OKAY [ 0.063s]
finished. total time: 0.238s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot erase modemst1
erasing 'modemst1'...
OKAY [ -0.000s]
finished. total time: 0.016s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot erase modemst2
erasing 'modemst2'...
OKAY [ 0.000s]
finished. total time: 0.000s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash bluetooth BTFM.bin
target reported max download size of 536870912 bytes
sending 'bluetooth_a' (400 KB)...
OKAY [ 0.016s]
writing 'bluetooth_a'...
OKAY [ 0.016s]
finished. total time: 0.031s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash dsp dspso.bin
target reported max download size of 536870912 bytes
sending 'dsp_a' (16384 KB)...
OKAY [ 0.359s]
writing 'dsp_a'...
OKAY [ 0.134s]
finished. total time: 0.492s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash logo logo.bin
target reported max download size of 536870912 bytes
sending 'logo_a' (2384 KB)...
OKAY [ 0.063s]
writing 'logo_a'...
OKAY [ 0.031s]
finished. total time: 0.094s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash boot boot.img
target reported max download size of 536870912 bytes
sending 'boot_a' (22301 KB)...
OKAY [ 0.546s]
writing 'boot_a'...
OKAY [ 0.599s]
finished. total time: 1.145s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash system system.img_sparsechunk.0
target reported max download size of 536870912 bytes
sending 'system_a' (524284 KB)...
OKAY [ 12.469s]
writing 'system_a'...
OKAY [ 4.152s]
finished. total time: 16.622s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash system system.img_sparsechunk.1
target reported max download size of 536870912 bytes
sending 'system_a' (524284 KB)...
OKAY [ 12.300s]
writing 'system_a'...
OKAY [ 3.593s]
finished. total time: 15.909s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash system system.img_sparsechunk.2
target reported max download size of 536870912 bytes
sending 'system_a' (524284 KB)...
OKAY [ 12.254s]
writing 'system_a'...
OKAY [ 3.605s]
finished. total time: 15.860s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash system system.img_sparsechunk.3
target reported max download size of 536870912 bytes
sending 'system_a' (490268 KB)...
OKAY [ 11.501s]
writing 'system_a'...
OKAY [ 3.374s]
finished. total time: 14.891s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash system system.img_sparsechunk.4
target reported max download size of 536870912 bytes
sending 'system_a' (441812 KB)...
OKAY [ 10.424s]
writing 'system_a'...
OKAY [ 3.039s]
finished. total time: 13.463s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash system_b system_other.img
target reported max download size of 536870912 bytes
sending 'system_b' (365228 KB)...
OKAY [ 8.329s]
writing 'system_b'...
OKAY [ 2.609s]
finished. total time: 10.937s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash oem oem.img
target reported max download size of 536870912 bytes
sending 'oem_a' (104376 KB)...
OKAY [ 2.448s]
writing 'oem_a'...
OKAY [ 0.733s]
finished. total time: 3.188s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash oem_b oem_other.img
target reported max download size of 536870912 bytes
sending 'oem_b' (19624 KB)...
OKAY [ 0.448s]
writing 'oem_b'...
OKAY [ 0.149s]
finished. total time: 0.613s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash vendor vendor.img_sparsechunk.0
target reported max download size of 536870912 bytes
sending 'vendor_a' (524284 KB)...
OKAY [ 12.952s]
writing 'vendor_a'...
OKAY [ 3.795s]
finished. total time: 16.748s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash vendor vendor.img_sparsechunk.1
target reported max download size of 536870912 bytes
sending 'vendor_a' (105284 KB)...
OKAY [ 2.559s]
writing 'vendor_a'...
OKAY [ 0.726s]
finished. total time: 3.285s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot erase carrier
erasing 'carrier'...
OKAY [ 0.016s]
finished. total time: 0.016s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot erase userdata
erasing 'userdata'...
OKAY [ 2.334s]
finished. total time: 2.334s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot erase ddr
erasing 'ddr'...
OKAY [ 0.000s]
finished. total time: 0.000s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot oem fb_mode_clear
...
OKAY [ -0.000s]
finished. total time: -0.000s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot reboot
rebooting...

finished. total time: 0.000s

____________________________________________________________________

### fastboot getvar all

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot getvar all
(bootloader) kernel: uefi
(bootloader) version-bootloader: MBM-3.0-evert_retail-7884113c1a-200826
(bootloader) product: evert
(bootloader) board: evert
(bootloader) secure: yes
(bootloader) hwrev: PVT1
(bootloader) radio: EMEA
(bootloader) storage-type: eMMC
(bootloader) emmc: 64GB SAMSUNG DH6DMB RV=08 PV=05 FV=0000000000000005
(bootloader) ufs: N/A
(bootloader) ram: 4GB SAMSUNG LP4x DIE=16Gb M5=01 M6=06 M7=10 M8=12
(bootloader) cpu: SDM630 1.0 (6)
(bootloader) serialno: ZY322V8K28
(bootloader) cid: 0x0032
(bootloader) channelid: 0x00
(bootloader) uid: BFF0F7E2
(bootloader) securestate: flashing_unlocked
(bootloader) verity-state: disabled (0)
(bootloader) iswarrantyvoid: yes
(bootloader) max-download-size: 536870912
(bootloader) reason: Volume down key pressed
(bootloader) imei: ***************
(bootloader) meid:
(bootloader) date: 07-06-2018
(bootloader) sku: XT1926-3
(bootloader) carrier_sku: XT1926-3
(bootloader) battid: SB18C20873
(bootloader) battery-voltage: 3812
(bootloader) iccid:
(bootloader) cust_md5:
(bootloader) max-sparse-size: 268435456
(bootloader) ro.build.fingerprint[0]: motorola/evert_n/evert_n:9/PPW29.1
(bootloader) ro.build.fingerprint[1]: 16-20-28/042db:user/release-keys
(bootloader) poweroffalarm: 0
(bootloader) ro.build.version.full[0]: Blur_Version.29.391.19.evert.reta
(bootloader) ro.build.version.full[1]: il.en.US
(bootloader) ro.build.version.qcom: LA.UM.7.2.r1-05300-sdm660.0
(bootloader) version-baseband: M660_30.77.01.101V EVERT_EMEADSDS_CUST
(bootloader) kernel.version[0]: Linux version 4.4.153-perf-g28e27408fc01
(bootloader) kernel.version[1]: (hudsoncm@ilclbld154) (gcc version 4.9.
(bootloader) kernel.version[2]: x 20150123 (prerelease) (GCC) ) #1 SMP P
(bootloader) kernel.version[3]: REEMPT Wed Aug 26 10:49:45 CDT 2020
(bootloader) git:abl: MBM-3.0-evert_retail-7884113c1a-200826
(bootloader) git:xbl: MBM-3.0-evert_retail-4149b81ab-200826
(bootloader) git:pmic: MBM-3.0-evert_retail-4149b81ab-200826
(bootloader) git:rpm: MBM-3.0-evert_retail-cf74f0b-200826
(bootloader) git:tz: MBM-3.0-evert_retail-7534c15a6-200826
(bootloader) git:hyp: MBM-3.0-evert_retail-7534c15a6-200826
(bootloader) git:devcfg: MBM-3.0-evert_retail-7534c15a6-200826
(bootloader) git:cmnlib: MBM-3.0-evert_retail-7534c15a6-200826
(bootloader) git:cmnlib64: MBM-3.0-evert_retail-7534c15a6-200826
(bootloader) git:keymaster: MBM-3.0-evert_retail-7534c15a6-200826
(bootloader) git:prov: MBM-3.0-evert_retail-7534c15a6-200826
(bootloader) git:storsec: MBM-3.0-evert_retail-7534c15a6-200826
(bootloader) frp-state: no protection (0)
(bootloader) ro.carrier: reteu
(bootloader) current-slot: a
(bootloader) running-bl-slot: _a/_a
(bootloader) running-boot-lun: 0
(bootloader) slot-count: 2
(bootloader) slot-successful:_a: no
(bootloader) slot-successful:_b: no
(bootloader) slot-unbootable:_a: no
(bootloader) slot-unbootable:_b: no
(bootloader) slot-retry-count:_a: 7
(bootloader) slot-retry-count:_b: 0
all: listed above
finished. total time: 0.219s
____________________________________________________________________

### fastboot devices

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot devices
ZY322V8K28 fastboot

I noticed that my commands were running without given a specific slot for each partition. Then I looked into Motorola's flash file for the Moto G Power and noticed that they were also using flash commands with a specific slot while my flash file doesn't. Maybe it's related to the MediaTek board but I don't know. I assume the mentioned error is not related to the fastboot version since Motorola also clearly states the slot on their own.