Encountered Cheater/Account Unplayable/NEED HELP

Hello! I require a deepdive into my account, and possibly a reset? I ran across a cheater who was playing as boss characters, one-shotting every player, after encountering this cheater, they proceeded to play animations to crash my game, then unlocked every achievement on steam for me, and now I cannot launch the game, when I do, I get met with a black loading screen with the flower in the bottom right corner. I can still hear and move my character in the background. PLEASE HELP, none of the advice I've come across has helped. Thank you!