Desktop #Linux will never be consistent, and, for better or for worse, you have to accept it.
The only way, if you want real consistency, is to only use apps that make use of dedicated libraries (known as "platform libraries") that are consistent with the design principles used by the desktop environment you use (just like #Libadwaita for #GNOME or #Granite for #elementaryOS).
It's hard (not "impossible") to make an app consistent with every existing DE and window manager.
You can try with any existing theme, it will always remain inconsistent, especially when certain apps *force* their design (Electron and CEF-based apps, Telegram, Steam).
#opensource #design #inconsistency