Yeah, I've been trying to set something like this up with a combination of iGPU and dGPU, which theoretically should be possible, but I certainly haven't gotten it to work as yet, and the documentation(and maybe the tooling too) leaves a lot to be desired. It offers ways to do some things, but very little in terms of more general explanation of all the steps, and the steps don't always apply as given(in my case, since I have pretty new hardware, they rarely apply at all). So I just have to sort of laboriously figure everything out. And it's quite a bit of dicking around to set up custom PVHs and such, again with lacking documentation.

I like Qubes quite a lot. But there's still a lot of friction if you're doing anything not supported by default.