> In what I would consider to be a fatal regression, GTK 4 just aliases <Control> and <Primary>, leaving the apps to do the work.

Gtk4 makes some many dumb decisions, that I always code new programs against Gtk3. They also deleted so many useful widgets and essentially said "We don't care implement it yourself". I can't afford my programs to become unusable just because they completely lost the plot, so I intend to keep using Gtk3 forever.