There are a number of GUIs to pick from, but maybe a good first try would be Lucas Chess. Lots of engines to choose from. The only warning is that there's a bit of a learning curve to figure out the GUI options and menus.
https://lucaschess.pythonanywhere.com/
I'm about 1100 blitz, fallen all the way from 1244, I'm too scared to play rapid after i hit 1305 last week. I play well (for my low rating), but get tilted after a single blunder (loss of a piece) and then play badly for the next few days. I'm so frustrated because all I do is study. Openings, Tactics, Endgames, you name it. Like this game:
I think maybe the best thing to do now is to "spar" with like 1200-1300 engine until I beat it blindfolded (not literally).
Yes, I'm aware chess.com have some, and lichess too has level 1 to 8, but I've played those ones a lot. I want to explore new territory.
It'd be very useful to me if anyone could reply. Thanks