Going back to earlier this year was a pull request for adding a GTK4 GUI back-end as an alternative to the existing and aging GTK2/GTK3 code. After weeks of work, this GTK4 support for the optional Vim GUI was merged.
This commit landed the GTK4 toolkit support that can be enabled with the --enable-gui=gtk4 configuration option prior to compiling Vim. The configure script currently favors GTK3 over GTK4 if not explicitly set.
Interesting the commit confirms that the GTK4 port was co-authored in part by Anthrophic's Claude.
Look for this optional GTK4 support in the next Vim release.