Despite not wishing you to have this trouble, I am somewhat relieved that the issue I am having is repeatable with another user. My issue sounds exactly like yours, and how you describe the boot process failing "right before the final shift into the progress bar" is exactly my experience. (also the verbose mode is very quick and on my 4k monitor the text is barely readable if videoed!).
To give you some context, I originally ran Catalina with OC 0.6.6 very successfully (I think around 2 years ago) on this board. The BIOS back then was F9g, and I used the depreciated Unlock MSR Using Grub Shell with success.
Then last year I updated to Big Sur on OC 0.7.4, keeping the BIOS at F9g. Everything still worked great, including Sidecar (using iMac19,1 profile).
I ran that system for a year (needed a stable build for work) and didn't decide to do any updates until recently (now the academic year is almost over). Over the last week I updated the BIOS to F9l (which is much better), and tested OC 0.7.9 - 0.8.1. When I discovered 0.8.0/0.8.1 not working, I queried it on this forum. Given 0.7.9 was working however, last night I tried installing Monterey on a separate SSD to my Big Sur drive. Despite one freeze during install (where I had to reset the computer), Monterey successfully installed. Everything appears to work fine as before, sleep/wake, Sidecar, airdrop and even that new feature in Monterey where you move the mouse over to the edge of the screen and it pops through into your iPad. As they say, it's like magic!!
Suffice to say, this build, thanks to Pastrychef, is very, very stable and reliable. Let's hope someone can get to the bottom of why the last two OC builds are not working.
