If the reboot loop follows the following pattern, then it is the known issue caused by broken NVRAM on certain X299 boards:
- You start Big Sur install, and it proceeds until "12 minutes left"
- It reboots
- A progress bar briefly appears, but then immediately disappears, and the system then reboots
- If you are booting in verbose mode and are able to see the messages before reboot, you will see lines saying "device is write locked"
- Further reboots will repeat steps 3-4 infinitely
If this is the case, then yes the only current working solution is to install Big Sur on another Hack - one that has working NVRAM - or a real Mac, and then transfer the SSD/NVMe to the X299 machine.
There is no problem running Big Sur on all X299 Hacks, once it is fully installed. But currently there is an issue actually performing the install or update on certain X299 motherboards.
Currently I am working on a method that might allow install on X299 boards with broken NVRAM. I'll be reporting back on that later today, I hope.