After the update on the forums yesterday the search box is no longer visible to all users, though technically it’s still there. If you want to search the forums, you have to click about 1/2 to 3/4 of an inch left of the three dots next to the character portrait. There is no indication that the search box is there or that there is anyway to open it.
Issue has been duplicated t-both using a Mac and Safari, and another user duplicated it on Windows with Firefox.