You want to find a file at a path in your project tree. But you've turned off the Project Tool. You could turn it back on, find the file, then turn it back off. But then you'll talk yourself into leaving it visible.
Use the Navigation Bar instead:
Activate the Navigation Bar with
Navigate -> Jump to Navigation Bar(
Use the cursor keys to get to the target directory
Speed search to select any subdirectories
Then, when your target is selected:
Find in Path(
Shift+Cmd+Fon macOS) to bring up the
Find in Pathdialog.
Just like you would in the Project Tool. Except, no permanent real estate lost and the Navigation Bar appears/disappears on command. All without touching the mouse.