I'm part of a Discord server that does exactly this. It's run by a math PhD, and he takes you through proof writing and up through the basic fields (algebra, analysis, etc) checking and vetting your proofs. It's great, and I've gone through multiple courses worth of stuff in abstract algebra, linear algebra and analysis. Currently working on some geometric algebra stuff.

You can message him on Reddit if you'd like and see if he'd give you an invite: CheapViolin