My favorite Mastodon 3.5.0+ feature is that if you have full text search on your server, you can search for
"from:username@anyserver.whatever foobar"
And it will filter search results for just posts made by username@anyserver.whatever. This is a further refinement to the existing search, so the limitation of "posts that either were made by you or you have favorited, bookmarked, or are replies to you" still applies. It's SO MUCH EASIER to search through my old posts now.