astro_ray

https://github.com/vinceliuice/Orchis-theme Try this theme. It has some fix for libadwaita app. Although, your issue could be because of flatpaks. Any chance your flatpak apps are not getting themed?

There is a hacky way to turn the background pitch black using css. There used to be an app that I think could change the background. https://github.com/GradienceTeam/Gradience

From my experience, dell has the best linux support for touch. Until Framework makes touch screens for their laptops maybe try going for dell.
Also, this is just my suggestion, research on your own as you are doing, since you know what you want best.

Definitely not what you want, but Gnome web (Epiphany) is GPLv3 according to flathub.