Upgrade to GTK4?

[MarioKart7z]

GTK2 is quite old at this point, and no other packages in my system require it. Most large GTK applications had already switched to GTK3 long ago, and they are now upgrading to GTK4 as well, now that it is considered stable.

https://www.gtk.org

Also, it seems that upstream Neko Project 21 has had an update earlier this year. At https://nenecchi.kirara.st the download for np2fmgen dates to 2024/01/01.

Side note: SDL3 is just around the corner as well https://github.com/libsdl-org/SDL