iMac 15.1 Graphics Fail Sequoia Upgrade - Feedback ?

Hey, all — was running Ventura under OCLP 2.4.1 on an i7-based iMac 15.1w/o any issues, but was time to upgrade to Sequoia. Updated “in-place” and the system booted to Sequoia fine, but after applying root patches and restarting, login wasn’t possible because the display was alternating every 5 seconds between solid black and the expected login screen.

I could see and control the mouse pointer while on the black screen, but on the login screen (light gray background) the pointer disappeared and no keyboard input was possible.

Rebooting into Recovery mode, I was able to use Terminal commands to back out the root patches. Rebooting brought up the gray login screen — this time with cursor and keyboard control. Of course, the computer is pretty much unusable without the graphics patches applied.

I repeated the patch removal/update process a number of times, and the result is the same, so it appears that there’s some sort of graphics driver issue caused by the patching process.

Interestingly, when running the patching process, there are two graphics patches being installed (See attachment), one for the AMD hardware card, and another for Haswell-CPU based graphics. Which is odd, because only the AMD card is present.

Any ideas, experiences, suggestions ?