Gnome theming broken (bug or feature?)

Hello to everyone.
As I see, user themes do not apply to all applications (example: nautilus, gnome-settings, gnome-calculator).
Is it normal? I mean basically the goal will be to use only two themes: adwaita light and dark?

I guess that you tried to apply a gtk3 only theme and this theme doesn’t support gtk4, all apps you listed are gtk4 apps. If you want to theme gtk4 and libadwaita I can suggest you to use Gradience (GitHub - GradienceTeam/Gradience: Gradience is a tool for customizing Libadwaita applications and the adw-gtk3 theme.)

Note that Gradience works by modifying the gtk.css file, which is unreliable and may break applications, or just not work at all with some applications. So use it at your own risk. Third-party CSS theming in general is somewhat of a hack.

The reliable way to do it would be for libadwaita to gain a true user theming API, and to change Gradience to adopt it. But this API does not exist yet.

Well, basically I understand, but if I might say some bad words here: backwards compatibility.
Without that, Gnome offers basically a flat black and a flat white theme.
I understand for some people it is not relevant, for me it is. I just went back to Gnome to have a nice desktop.

Why does Gnome break his own stuff twice a year?

There cannot be backwards compatibility, GNOME apps did not officially support those themes. The flat black and flat white themes are the only officially supported ones.

There could be backwards compatibility, if wanted. Gtk4 supporting gtk3 and gtk2, and so on.
Sorry, end user poit of view. (Probably and important one?)

No, that’s just not possible. GTK4 and GTK3 have different internals, and GTK2 doesn’t even use CSS.

So guys, I got a taste of gnome after eight years, and I’ve quit after one week. Again. Still the same: breaks stuff after every update, and does not give a darn about user input. Bye, probable we meet again after eight years, I’m not a huge loss. (Just like thousands of users like me.)