currently Nostur only uses local search and it always saves your own posts in the local db, so if you always used Nostur you can type “Oshi keyword” in search and it will find your posts, I use it all the time to find anything I ever posted.
but if you posted from other clients Nostur may have missed those so as a workaround you could visit your own profile first and scroll through all your posts so it will save them all, and then use Search after that.
Maybe I’ll add a “Download all my own stuff” some time to make it a bit easier.
