Hi. So ... here's the status update, and a few more coments.
TLDR: NVMe controller on the motherboard is gone. Not dead, but worse, as it even corrupts the filesystem. The fix ? PCIe NVMe adapter.
Starting from where we left off, first thing i did was revert to 6.10.3. Good idea, but ... same errors. Very, very odd. Did a few searches, and most of them referred to a bogus motherboard error, which looked the same. The difference here is, their motherboards were new, mine isn't (4 years old). Still, I decided to get a PCIe to NVMe adapter board, and ... it works. No errors, all fine. The system still needed some repairs, but I managed to repair it without major issue. And no more corrupted blocks.
Now I'm trying to reach ASUS to find out why I can only see one NVMe and not the two on the adapter (already went to the BIOS to check). Might even get my W11 VM 100% back, but let's see. I do see a light at the end now, just hope it's not a car or a train.
Again, thanks for the help.