Thanks for that guide - I actually found it referenced somewhere else and followed it pretty much to the letter with the most recent Win10 VM attempt (stopping short of the virt-manager section). After reading countless forum posts, articles, and watching videos I've seen everything all over the map recommended for any possible scenario (SeaBIOS vs OVMF, Q35 vs i440fx, use vbios or don't) - the community doesn't seem to have any reliable consensus aside from 'use whatever works' & 'try everything' which is infuriating haha.
I may not be having the exact same issue, in fact I don't think anyone in the world is having my exact issue since my hardware configuration (and most folks) are rather unique, but I am on 6.9.1 and I cannot get GPU passthrough working for the life of me despite following every guide I could get my hands on.
Behold: