It helpfully says "1-0 of 2" notifications are shown, which in reality means the list is empty.
It's from some scam repos that mentioned me but were deleted before I could clear the notification.
Am I the only one bothered by this? How do you get rid of the dot? ;)
Or maybe disabling / re-enabling notifications.
Install the GitHub CLI ("brew install gh" or similar), authenticate with your GitHub credentials ("gh auth login"), then run the following:
gh api --method PUT -H "Accept: application/vnd.github+json" /notifications -F read=true
Blue dot gone! :-) This marks all notifications as read, which clears the phantom notification from the deleted account.