https://blog.gtk.org/2020/12/ - GTK4 development started in Oct 2016 and was released in Dec 2020, two years ago.
I have no idea the effort involved in building an LCL widget set interface, but maybe consider going straight to GTK4 and dropping GTK3? Could be better than being always in catch-up mode.
Not really. GTK is notorious for changing their API also after a release. During the years their API stabilizes. It is actually a good strategy if developers know it and understand what it means.
For LCL bindings it means we should
not jump to the latest GTK version right away.
GTK3 has been stable enough for few years. The slow development of LCL bindings is caused purely by lack of resources. Apparently nobody wants it badly enough.
A (big enough) bounty could help but it is not certain. It still requires somebody with the skills, time and motivation to do it.
Somebody could say that a stable API is the most important priority and GTK should change their API.
OK, a stable API has its merits but what if you continue it for decades? For example Xlib is very stable but how many people want to use it?