Yesterday I needed to look at some things without being "myself", aka not logged in, and tried to use the search bar on top to find the thread I was looking for.
It didn't work. I think I was using internet explorer , for sure I was on a Windows desktop. I was logged in on Chrome on the same desktop at the time.
Weird! I just tried searching while logged out, both with the search bar, as well as with the Advanced Search. Both gave me results.
It could be you were searching in the search bar while in a specific forum. If I'm in Earthship forum, and search for "yarn," I'll probably not get any results. For some reason, the search bar defaults to searching just the forum you're in for what are searching for.
Maybe go to https://permies.com/forums and try your search there? Or go to the relevant forum and search for it there?
That's surprising -- the search engine here is remarkably robust.
I ran a few tests. It seems to work perfectly.
Config: Linux Mint 20.1, Chromium, third party cookies blocked, running uBlock Origin extension in its standard configuration.
(And of course before testing, Ct-Sh-Del, Advanced, select all, delete everything for all time, restart browser.)