Wow, I never saw this, so sorry! I made this game in like, I think a week with Godot 3.5, and yes, it is a prototype as you stated!
I would love to redo this project in Godot 4, but it would have to be with bigger sprites, undoubtedly, to fix a lot of the issues you've mentioned. I just couldn't fit certain icons and numerals with the limited size (I tried quite a bit). I'm not completely satisfied with the X for 10 or characters for the suits either, haha.
As for pausing, restarting games, etc. I totally agree! I'd also like to implement an undo and hinting system, and maybe a few other QoL features and juice (sound effects, wobbles, all that). I really want to remake this game with my full vision in the future - little ghost RPG with solitaire. Will have to see about working on refactoring this in Godot 4 in the near future. :]