@KaKi87 I do not have any gnome app to try, but can you force the display of the title bar with a Kwin rule? Press alt-f3, select More actions - Windows rules. The +Add Property, and choose No title bar and frame [Force] No.

@D_Air1 It is not just gtk4 apps, of which I don’t use any, but also Firefox and Thunderbird and many others work but have glitches.