So libadwaita is basically a library that provides a set of user interface elements and patterns for building GNOME applications. It uses GTK4, but the main difference is that it has the specific Adwaita theme "baked in", and that you "can not change it".
Of course, you can change it. The gnome folks just made it harder than normal, by not making it follow the established theme folder configuration. But in the end, all you have to do is create a symlink. That's basically what this tool does for you: https://github.com/odziom91/libadwaita-theme-changer
But now I found another solution, which does make libadwaita follow the selected GTK4 theme, and it's called "libadwaita-without-adwaita"
Great stuff! One less hoop to jump through when I want to enable the Skeuos theme 😄
Here's a Flatpak story: The other day, my best friend told me that he had switched to Linux! Arch Linux with KDE Plasma, a noble choice in my opinion. He's a smart guy, but he was having some issues that he couldn't figure out: Firefox' maximise and minimise buttons were missing, drag and drop from archives wasn't working, his selected theme wasn't applied everywhere, and many other small issues I can't remember now.
I tried reproducing his issues on my machine, but everything worked fine for me. We were confused. Is there missing libraries? We went through packages to find out what my system had that his didn't. It was weird, everything was kinda working, but the devil was always in the details, for every single app.
And then we found it: All those applications he had issues with were Flatpaks! He simply didn't pay attention when installing them through the Discover store. He didn't even know what Flatpak meant.
I helped him remove Flatpak from his system and install the system packages instead, and all issues were gone.
Man, Flatpaks suck. How does anyone prefer Flatpaks over system packages? How does anyone think this was a good idea? Stop trying to invent new things to solve old problems and instead go back and fix the problems.
Containers, Flatpak, Immutable distros, it's all wasted effort. There is no magical solution that will solve all our problems. The only way to solve all problems is by solving each problem individually one by one. And that is exactly what countless distribution and package maintainers are doing on your behalf every single day.