GTK 4.0

GTK 2 is on RHEL 7's list of Compatibility level 1 packages[0].

This is a very short list of packages, and gtk2 and motif are the only GUI toolkits in it.

For RHEL 8, gtk2 moved to Compatibility level 2, and notably there are no GUI toolkits in level 1 any more, while level 2 has gtk2, gtk3, motif, libXaw, qt5-qt5base.

So at a minimum Red Hat has promised to support gtk2 until RHEL9 EOL for paying customers.

[0] Compatibility level 1: APIs and ABIs are stable across three major releases (starting with RHEL 7)
https://access.redhat.com/articles/rhel-abi-compatibility...

[1] Compatibility level 2: APIs and ABIs are stable within one major release
https://access.redhat.com/articles/rhel8-abi-compatibilit...