I got hear searching for this feature (that I assumed was here).
What I imagine is a hotkey that jumps from a note pane (or other) directly to the file tree. Then the up/down arrows work like they do now. Then add the basic features of file explorer: ENTER to open that folder (for arrow navigation) and BACKSPACE to exit/close the folder.
For consistency their ought to be able to jump to the right pane as well. It wouldn’t be bad to have a way to go back and forth between files and search in the left pane (without a mouse).