@Lunch Unfortunately this is the same for me too with an MSI Trio RTX 3080ti in the top slot of x570 Taichi. Any luck since your last post? I'm away from my server at the moment, but want to experiment some more once back. I've had no issues with other GPUs in the same system booting to Windows10 (passthrough disk).
I tried booting to Windows, saving VBIOS via GPU-Z, editing out the top part, and saving as .rom and .dump --- unfortunately neither worked. Thankfully SIO has at least provided some kind of work around.