I had the same problem when I relocated my Dev folder to a new drive. I couldn’t understand why those projects in the Dev folder I relocated no longer showed up in the Launcher under My Projects. The solution was just to make another Unreal Engine 5 project in the same Dev folder as my other projects and once I exited the new project, all my other projects reappeared.
Just to say I had the same issue, the above way of editing the GameUserSettings.ini didn’t work for me, but this method did. Thanks!