> Does this mean GTK2 and GTK3 are... to be avoided for new projects / dead?
not dead but... here's for instance how Wireshark looked on macOS when it was using GTK :
https://blog.wireshark.org/wp-content/uploads/2013/10/osx-x1...
and here's how it looks now that it is using Qt :
https://news-cdn.softpedia.com/images/news2/wireshark-3-0-re...