QA needs to be paid as does programming. I imagine some people have a passion for it and could build automated qa tools around open source products. Say a gui tool that automates clicks on kde or gnome widgets. That would be quite a challenge in itself.

As for ux, open source is not a job. Ux folks are told my product managers to enshitify things on daily basis.

I imagine open source can provide a safe haven form all that and let people run wild beautiful ux and uis. Imagine someone working on the ux of a linux distro aimed at making onboarding of casual users easier.

Imagine a group of people putting together a nice set of guidelines for ui and ux similar to how apple has guidelines.

I think these are two areas where linux (distros) have gaps.