Similar issue here.Hey, i don't know why but for me i couldn't get the commands to work. Even just fastboot set_active a didn't work.
So i just spent 3 hours unlocking oem then trining to install then it not working, corrupting the device and fixing it. Now im back on stock rom. I just wonder, why on earth did even the basic First command not work ?
What works:
Code:
fastboot set_active a
fastboot flash boot boot.img
fastboot --disable-verity --disable-verification flash vbmeta vbmeta.img
fastboot --disable-verity --disable-verification flash vbmeta_system vbmeta_system.img
Everything else either isn't recognized as command or my usual issue of it not finding that partition (e.g. for some reason the system thinks that the system partition does not exist...maybe a driver issue? I am at a loss). But I was already stuck trying to root the phone with the stock firmware, always ending up in a bootloop despite doing every step as listed.
Any idea why those commands do not work? Did you use anything special to make them work?