I have two suggestions:
1) I recently did a fresh Windows 11 Pro install and got WHEA errors - about 20 per minute non-stop in HWInfo. I installed all of the drivers myself, carefully. Then I did another install using Armoury Crate and the errors completely disappeared. I still don't know what was wrong or the true reason for that. I suspect that perhaps one of my Intel drivers got corrupted.
2) Risers are known to cause problems sometimes. I would remove the riser and try plugging the GPU directly into the motherboard as an experiment
If everything is running at OK at 4800MHz memory speed, at least you have a point from which you can start to make gradual changes. If points 1) and 2) don't help, I think I would be focusing on memory stability at this stage. You can swap sticks, vary voltages etc etc. but go slow. Good luck.
Z690 Hero, BIOS 2305, ME Firmware 220.127.116.116, 7000X Case, RM1000x PSU, i9 12900K, ASUS TUF OC 3090TI, 2 x 16GB Corsair RAM @ 5200MHz, Windows 11 Pro 22H2, Corsair H150i Elite AIO, 4x Corsair RGB fans, 3x M.2 NVME drives, 2x SATA SSDs, 2x SATA HDs.