I made downgrade to oreo to release the bootloader, and I proceeded with your steps but I failed, I could not change the slot, restart fastboot to change it and I did it but the recovery never started again, every time I did it it blinked and stayed in loop , as I read you said something about not updating to android 10 but I was in oreo, now I try to install pie stock and see if from there I can install the rom
Update:
nope i cant boot twrp after flash slot A and reboot to bootloader twrp dont boot anymore