I don’t think there’s a separate build with Nvidia patches now (at least on the AUR), as they’re included/fixed upstream. Still plenty of config and environment variables to set on Nvidia. And the new Nvidia beta driver, 555, should fix flickering in xwayland windows that was caused by a lack of explicit sync support. It’s been working well for me so far!
I’m sorry to hear you’re having trouble!
Regarding the vainfo thing, at least on Arch, the Nvidia vaapi driver is a separate package. I’m not sure what the equivalent is on bazzite, but that’s likely why vainfo doesn’t show anything. And you should still be able to use nvenc anyways, which sunshine will choose before vaapi.
Is moonlight able to see the computer on your network? And in sunshine’s web interface under the “troubleshoot” tab, there’s a log. Does it say anything that might help?