I’ve used shift+enter to search backwards through text files for who knows how long. I’m extremely surprised that obsidian doesn’t allow this, nor does it allow us to change the shift+F3 functionality to shift+enter. Oddly enough using enter w/o shift works to search forwards within a note.
I don’t believe there is a Search backwards command to bind the hotkey to. It definitely sounds like useful functionality that I would take advantage of if it existed. Upon searching, I found your feature request: Searching backwards within a note