I am on gnome machine (Dell I5 desktop 24inch dell monitor 4gig ram Intel graphics) shotcut repo and flatpak did have problems but got flatpak working on mine by setting shotcut theme to fusion light and changing the other two settings to mojave-light and papirus-dark. No luck with repo shotcut missing timeline icons. (Seems be working ok like this) Weird stuff
Seems to have straightened itself out for some reason can change anything now and works (flatpak)
Hope this helps someone out all the time I have to devote to it right now.
Repo shotcut cant get to work at all (removed flatpak installed repo)