GTK4 is 98 MB RSS on Linux. Or just 24 MB for GTK3.
example-0.c (fits both GTK3 and GTK4) from https://docs.gtk.org/gtk4/getting_started.html
example-0.c (fits both GTK3 and GTK4) from https://docs.gtk.org/gtk4/getting_started.html
Not sure if it had something to do with my env (NixOS), but either way it was a turn off since I see 20-30 MB with GTK3 which is about the size of my full-featured macOS AppKit apps.