Use case or problem
When you want to search across all files, it would be much easier, both on desktop & mobile, if the search box was located at the top of the file list (similar to the default Notes app in iOS).
Proposed solution
Move the search bar to the files tab and put it above the list of files. Then, when you start a search, the list below filters dynamically as you type. Hitting escape on desktop (either require Esc to be hit once or twice not sure which one would be better), should exit the search and return you back to the list of all your files.