check the catalog, GTK2 port, to see what depends on it.
I checked the first one, hexchat. It actually still requires gtk2 although they are working towards gtk3 support.
The rest of the ports on that list need to check to see if they can move to gtk3.
Here's a list of ports that currently depend on GTK+2 in RP. Their status will be added after each has been checked.
[x] dia:standard Dia is Dia ... There's (some) activity in the master branch but no tag / release happened in over a decade. Code in the master branch uses GTK+3 and there has even been talk about GTK4 in the issues. I'm not holding my breath for it, though. Unfortunately it's useful software.
[x] gimp:standard Porting to GTK+3 has been a major task but was completed in mid 2023. Upcoming version 3.0 is meant to be ready for GTK+3 but the release has not happened yet (despite being expected for late 2023).
[x] gmrun:standard Requires GTK+2 and there's basically no hope it will ever transition. The project hasn't had any release in two decades and the source on sourceforge is still in a CVS repo (which SF stopped supporting in 2017). Obviously nobody stepped up to adopt the project.
[x] graphviz:standard Can be built without GTK+2 but that means losing __libgvplugin_gdk__. Maybe override the port like this via unkindness and do an exp-run to see if it's actually used by something or just was some GNOME 2 thing? Various sources on the net seem to indicate that it's optional and people could just ignore warnings related to it not being available. A little weird, though.
[x] gtk-murrine-engine:standard This is completely tied to GTK+2 and will eventually be retired together with the toolkit. It's only a reverse dependency for Xfce's official theme. Likely to be dropped when Xfce eventually stops requiring GTK+2.
[ ] gwenhywfar:standard
[x] hexchat:standard
[ ] leafpad:standard hard requirement for gtk2. replace with GTK3 fork l3afpad see repology
[ ] libcanberra:standard
[ ] libglade:standard
[ ] libvisual-plugins:standard
[ ] libwacom:standard
[ ] mtr:x11
[x] ~parcellite:standard~
[ ] pidgin:standard
[x] ~pinentry:gtk2 This is meant for purely GTK+2-based desktops. We don't have any of those. Let's just drop this variant.~
[ ] postgis:standard
[ ] qemu:standard
[ ] smpeg:standard
[ ] thunderbird:standard
[ ] wxWidgets30:gtk2 This is required for perl-Alien-wxWidgets and perl-Wx-Scintilla which is required for PADRE (perl IDE) which hasn't seen a release in 11 years. Requires dropping PADRE is which something that should be considered seriously.
check the catalog, GTK2 port, to see what depends on it. I checked the first one, hexchat. It actually still requires gtk2 although they are working towards gtk3 support.
The rest of the ports on that list need to check to see if they can move to gtk3.