@BrodieOnLinux Thats the absolut best decision, in my opinion. In the long run you will otherwise either hold back the other project or break your project. As long as there are moving parts. And that is, if you agree on a direction.
To fork GTK3 apps is also a good thing. GNOME GTK4 is tied to libadwaita. So going forward without platform library, or an own (non-fork) could be more work.
I'm just a bid sad that this move happens only now. It's a little late. Still nice to see!