GTK4 port status?

On behalf of the Circle committee, I was wondering what the status of the GTK4 port is (e.g. missing features in the platform, technical debt, lack of time). We will start requiring GTK4 at some point in the future, so we're reaching out to the last few remaining GTK3 apps to understand if there's something we can help with.

If you're struggling to find time for the app we could help put out a call for contributors/co-maintainers, this has worked out well in other cases :)

This is a status request about the GTK4 port, but it names no files, tests, or entry points. Start by reviewing the repository and its GTK3 implementation to identify the port's current state and remaining scope. The issue is done when the status and any concrete next steps are documented.

Written by the indexing model from the issue text.