...but then feeling out of place on GNOME / GTK4 / LibAdwaita-land

Linux is a mess, but at least it's unapologetically so.

They've got unified themes that make GTK and Qt applications look nice alongside each other. Users who care will be using those. Users who really care might refuse to use your application because it isn't the toolkit they like, but you shouldn't lose sleep over satisfying such particular and demanding users. They're not paying you anyway.