Reply to post: "GTK+ 3 had removed some features they'd been depending on"

"GTK+ 3 had removed some features they'd been depending on"

That is a bit of an understatement "some" (or "a lot") is relative I guess. The tabbed dialogs being a bit "jarring" is more accurate. There are many significant Gtk changes that will impact the Pi, especially if you have limited screen real estate. Gtk+3 removed the toolbar widget as well as the menu widget. (which to a large degree is why you will see menu entries have grown taller and many applications can no longer fit the same number of icons in the new object used as a toolbar without the bar ellipsizing with spillover in '...' menu to the side).

Few apps properly apply the new gtk.toolbar class style which mitigates the toolbar icon appearance somewhat with set_style() -- but there is little motivation to do so since much of the gtk.toolbar class style is deprecated now like to be removed in Gtk4 (no + in the name anymore). The Gtk change is one of the reasons the direct Buster->Bullseye update for Desktop installs isn't recommended (though there are more reports of success than failure) And with a Pi 3+b, I'm not anxious to have my nicely themed desktop revert to one with jarring square corner tabbed dialogs...