Hi, yes it’s there & I see the file referred to in the help doc (“For users who had issues migrating data from Brave Muon to Brave Core”):
The most recent date changes for the files in that folder, including the one above, show January 22.
I don’t know what happened then. It’s possible that was when I first went back to the non-Dev version to run it in parallel with Dev (since I was having problems with Dev).
I don’t recall doing anything other than running it from the Dock icon but it’s possible I responded to a prompt to update it.
I never saw any mention of Muon v. Chromium, though.