To help others, here is the solution to my problem:
I downloaded some firmware versions available here (https://xdaforums.com/t/help-with-a-s805x-box-official-firmware-update-borked-it.4646963/post-89791881) and used Android's Recovery mode to return the version.
I clicked on "Apply update from" and used the .zip file for this. With this, the restart loop problems were resolved and now I can run Armbian directly from the pendrive. I'm trying to install it directly on the eMMC and I hope it works, I'll come back here with news.
@ssdm2nvme Hi, whats up?
I tried everything you recommended, including following some other tutorials beforehand, but I still can't get past the TV box's "BIOS" screen.
It keeps restarting repeatedly, and I can never actually access the system. Do you have any idea what it could be?