same.. 2020 27" BTO iMac. bricked it. No volumes detected on reboot, but bootcamp still worked as normal (well it did until I picked "restart in macOS" from the menu). I tried DFU revive which looked like it completed normally but resulted in endless reboots into internet recovery. I'm resigned to having to do a "do over", but is there ANY way to recover my data? I'd hate to lose all my stuff from my last backup which was some time ago. Oddly the install went just fine on my MBP

Is there any support for beta installs? If so, how do you access it? (I submitted a bug report already_ Same problem for me though. Bricked my 2020 iMac 27". Worked fine on my 2018 MBP though. I tried everything including revive, internet recovery, target disk mode, safe mode... Nothing. Revive looks like it works, but instead of booting into the recovery partition, it goes to internet recovery then deadlocks.. Does internet recovery, reboots, does internet recovery ad infinitum . There's some files I need to recover too. Interestingly, the Bootcamp partition still works fine, so now I have an Apple branded PC :( I just need to get access to the disk so I can pull a few files.

Same. Since my 2015 was on Big Sur, I can't open my photos on the new machine due to upgraded library. Guess its just wait a bit. Now that I know its not just me, no biggie.