Which “Search and Hotkey” plugins were you using?
Of course there may be a plugin that can do it, but I haven’t come across one that allows double modifiers (Shift + Shift) in Obsidian.
Is there some software outside of Obsidian where you’ve set this?
I’d try in the Sandbox vault and the other troubleshooting steps to see if it’s something about that vault, Obsidian itself, or something outside of Obsidian. You could also paste your “debug info” (cmd/ctrl + p → Show debug info ) here so folks have a better idea of your setup.