@SepehrRS has started developing a beautiful Sudoku game using GTK and Libadwaita, and he's planning to bring it to GNOME Circle soon.
I've contributed to the project, mostly with the app's UI, logo, and making sure it meets GNOME Circle's app criteria.
You can install the app from Flathub or contribute on GitHub by opening issues and helping make it better.
https://flathub.org/apps/io.github.sepehr_rs.Sudoku
https://github.com/sepehr-rs/Sudoku
P.S. Sepehr has also been helping us triage bugs in Drum Machine, thanks a lot!