They decided to make GTK4 apps exclusive to the desktop environment for which the app was built for. You could use it outside the intended DE but it will look alien.
They have done pretty much the opposite - they added a proper API of theming instead of having a stylesheet override. GTK didn't really have themes before, so this is quite nice.
> They have done pretty much the opposite - they added a proper API of theming instead of having a stylesheet override.
That's not theming, that's just changing accent colors in the same theme. If I don't like dark background color, I can't change it. If I don't like the light background color, I can't change that either. All I can do is change accent colors.
The entire GTK and GNOME ecosystem is heading towards Android like customization and theming, which is basically non-existent at this point.
GTK4 apps aren't meant to used outside of the platform for which they're built for. If the GTK4 app in question is built using libadwaita, it's meant to use only inside GNOME. If it's built using libgranite, it's meant to used only inside Pantheon (from elementaryOS).
Of course, you could use it in KDE or MATE or anywhere else but it would look completely alien with different themes and, potentially, different fonts and icons. You can't set your own theme without resorting to hacks.
If someone has come across a GTK4 app which isn't restricted to a specific desktop environment, let me know. Meanwhile, I won't use any GTK4 apps in existence.
