Kinda hard since we don't know what you've watched already, but here are my recs:
Ex- Machine: Pretty solid movie, has some interesting ideas and a cool premise, can be a bit slow, but some consider it to be one of the best sci-fi movies of all time (it's not, but it's still good)
https://www.imdb.com/title/tt0470752/
Taxi Driver: My favorite movie of all time, it's the incel anthem for the people that completely missed the message, but everything about this movie is a 10/10. People have said that Joker is heavily inspired by this, and in a way you can see that, but I don't agree all that much.
https://www.imdb.com/title/tt0075314/
King of Comedy: Same director as Taxi Driver, this is 100% the inspiration for joker. Not saying joker is a carbon copy because its not, but Joker does a lot of the same beats as King of Comedy.
https://www.imdb.com/title/tt0085794/
Oldboy (2003): If you do watch it, watch the 2003 sub version. This is a Korean movie, amazing, you mightve watched already but its just great. Its a lot more action focused than thriller so beware of that, but it is categorized as an action/thriller, I dont think thats very accurate tho
https://www.imdb.com/title/tt0364569/
Good Time: Just a good heist drama movie. Give it a watch
https://www.imdb.com/title/tt4846232/