Like I'm trying to find my own comments and clicking the comment part on your profile just takes you to a blank page with a search thing.

The best I've found is the search comments dropdown that shows you people that have replied to you.

Try:
_ user:Timo4545

That worked for me. Why is the underscore-space necessary and also is there a way to do that for forum posts? I can find all the posts that quoted me but not all of my posts.

It's funny because if you go to a user page and click the "comments" link it takes you to a search of user:Username without the underscore which obviously doesn't work

Does this still work?

This worked on the old site. As far as I know, the current site has no way to search comments.