Atari sent me this last year.
Hello,
There are two potential fixes to being stuck in an update loop.
1) Boot with a keyboard attached, holding down the ESC key. Go into boot manager. You will see three options. Select EFI Embedded MMC Device 1 (TA2932). The system will reboot.
2) If that does not work, you will need to manually flash the box with an OS image from a USB stick. It can take a bit of time to download and write the file to the USB drive but is otherwise a very straightforward process. Please follow the instructions in the Google Document inside this folder: https://drive.google.com/drive/folders/1pgC39vlSaK-8am4cbGKLgQrnKILRU1iK?usp=sharing
One of these two solutions has worked for the majority of users who have run into this issue.
Kind regards,
Atari VCS Support