Migrating from GTK 2.x to GTK 4 [src]
If your application is still using GTK 2, you should first convert it to GTK 3, by following the migration guide in the GTK 3 documentation, and then follow the GTK 3 to 4 migration guide.
If your application is still using GTK 2, you should first convert it to GTK 3, by following the migration guide in the GTK 3 documentation, and then follow the GTK 3 to 4 migration guide.