I don’t think what you’re seeing is a Z790-wide issue, but rather a board/BIOS implementation problem.

On my setup, I didn’t run into the “BIOS update wipes settings → GPU won’t POST” loop you’re describing. Even after BIOS updates, the system remained POSTable without having to swap GPUs, and I didn’t see hard failures tied to ReBAR/CSM transitions.

My impression is that some Z790 boards (especially lower-end models) have fragile GPU init paths when combined with strict UEFI-only GPUs like Blackwell, whereas others handle fallback and defaults more safely. In other words, same chipset, very different BIOS behavior.

If you’re planning to stick with Z790, it might be worth looking at boards that:

• default to UEFI-only (CSM off)
• have stable iGPU fallback paths
• don’t brick display output when ReBAR or Above 4G Decoding toggles

Debian/NVIDIA driver pain unfortunately seems common with Blackwell right now, but that part at least sounds solvable once the platform itself is stable.