Oftentimes I want to link to an old post of mine, or a thread that I posted a reply to in the past. Unfortunately, Discourse doesn't seem to have a way to search this, I think? Adding @ExpHP to the search query seems to limit it to threads where I am the OP. I can also search threads I've read, but I read a lot of threads, so that often produces too much!
I personnally use bookmarked threads a lot for this very function; which ends up leading to me very narcissistically bookmarking my own posts
There is also this option:
When you are in your profile, activity, replies and maybe ctrl + F. link
You can also download them and search there.