If you're here, you may have had a similar problem to me recently. The problem in question is where projects won't show under "My Projects" in the Epic Games Launcher. This also causes issues when adding Marketplace Assets to your project as the launcher won't show them in the Add To Project Dialog.
I may be wrong but it seems the Epic Games Launcher had an update at some point to change how it works. From what I remember it used to always search on your C:\ drive for projects. Then it would add other projects to "My Projects" if they were opened using UE.
To add new search directories to the Epic Games Launcher you'll need to change some configuration options.
So, first, open your File Explorer and go to your Local AppData folder by typing %LocalAppData% into the Explorer. You'll want to go to:
Which then you'll find a few files, one of them will be called GameUserSettings.ini. Notice how the files are the same as the ones UE produces, this is because the Epic Games Launcher runs on Unreal Engine behind the scenes, which I think is pretty cool.
Open GameUserSettings.ini and at the top of the file, you should find the Launcher section. In the image, you'll see two lines that set CreatedProjectPaths. I created the second line since that's where I store my projects.
Just add a second line, or change the first, to where your projects are stored and they should show up in the Launcher.
From what I understand, you can add as many Project Directories this way and they'll show up in the Launcher.
Why it doesn't detect directories automatically anymore is beyond me.