The sprites and animations are also made by me, so it's programmer art, don't ask me too much (I think the graphics are decent, tho, but nothing as an artist's work)
I maybe address the shop problem in the future, because what u say is pretty valid.
And about the performance, I really thought it was the android version while I was reading, but since is the windows version, it may be because of your old software. The game is fully compatible in Windows 10 and 11.
I'm gonna port the game to a newer game engine soon, and maybe in that software, exporting to windows will result in a more stable version, even for old hardware.