If you press Ctrl+P and start typing the filename, devtools should find the file and list it below; clicking it opens it. I use that often when files aren't listed in the navigation pane for whatever reason.
You see a message about this when there are no open editors:
Here for instance I've opened devtools on this SO page, opened a file (just to show that Ctrl+P works even when there's already an editor open), and typed the first three letters of "jQuery" since I know SO uses jQuery:
As you can see, it found jquery.min.js
for me.
This is often handy even when files are listed in the navigator.
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