[Moto G7 Play Questions & Answers] andyhoy:
Exinu, thanks for your continued assistance. As it turns out the fastboot/adb version I was using didn't include the "set_active" command (I don't think it was a path problem as I was always typing commands from the in directory where the ADB software was downloaded). As I had tried to follow a number of different tutorials of the course of several weeks, some for the G7 play, and perhaps some for the G7 and others generic, I think the place on the web that I went for the original ADB package (or the ADB version) was the problem. I also found another copy of ADB on my drive (downloaded weeks ago) that was titled "Minimal ADB and Fastboot", and as it turns out, that version DID support the set_active operand (from the fastboot --help command). So, I was able to return to your initial directions to set the active partion to b as initially instructed (see below, but the phone also shows that the set_active:b command seemed to process without error). However, I was not able to do the next step of flashing the TWRP. I tried the TWRP version you suggested and linked to (the dirtyport version) and then also the "channel" version, which I understand to be designed for the G7 play, unlike the "river" version. In either case (dirtyport or channel) I get a new/different "usage: unknown command" error, as seen in text pasted below:

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot set_active b

Setting current slot to 'b'...

OKAY [ 0.176s]

finished. total time: 0.178s

C:\Program Files (x86)\Minimal ADB and Fastboot>dir

Volume in drive C has no label.

Volume Serial Number is EC2B-BC54

Directory of C:\Program Files (x86)\Minimal ADB and Fastboot

2020-11-27 01:42 PM <DIR> .

2020-11-27 01:42 PM <DIR> ..

2018-01-11 06:53 PM 1,784,320 adb.exe

2018-01-11 06:53 PM 97,792 AdbWinApi.dll

2018-01-11 06:53 PM 62,976 AdbWinUsbApi.dll

2015-08-09 01:50 PM 29,882 cmd-here.exe

2018-01-11 06:53 PM 853,504 fastboot.exe

2020-08-17 02:31 AM 1,456,678 logo.bin

2020-08-15 11:25 PM 27,848,704 twrp

2020-09-03 02:52 AM 27,133,952 twrp-dirtyport-g7play.img

2020-08-16 01:12 AM 17,307,289 twrp-installer-3.4.0-0-river.zip

2020-11-17 04:21 AM 23,298,048 twrp-moto-g7-play-channel-android-10.img

2020-08-15 11:25 PM 27,848,704 twrp.img

2020-11-27 01:27 PM 5,004 unins000.dat

2020-11-27 01:26 PM 717,985 unins000.exe

13 File(s) 128,444,838 bytes

2 Dir(s) 28,010,246,144 bytes free

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot twrp-dirtyport-g7play.img

fastboot: usage: unknown command twrp-dirtyport-g7play.img

Granted, I'm not a command line expert, but I have been playing with computers since the TRS-80 and the C64 and Apple IIe, and 8086 DOS stuff, and used to do QBasic programming as a kid, so in most cases, I can usually navigate myself through some hairy computer instructions to do whatever I need to do, unless the instructions themselves are hairy. I find that the Android Dev forums are predicated upon some knowledge of those platforms and are a rude awakening for those unfamiliar with the development history and architecture. Obviously, I'm going to extremes to try to de-google an Android phone (frankly I would be happier if there was more stuff on the market that already was preinstalled), as this google censorship and proposed contract tracing stuff is just getting out of hand and going too far... so this is my way of fighting back. I'd rather know nothing about ADB, but here I am. ;)

Is there any chance you know how or why I am getting the "fastboot: usage: unknown command twrp..." error above, or how I can resolve it?