The Epic Launcher on Windows stores its games in
C:\Program Files\Epic Games. However if you copy a game from one computer to another, the Epic Launcher on the new computer won’t recognize it or let you play it. Super annoying if you want to avoid re-downloading 60GB of stuff you already have a copy of. (Steam does not have this nuisance.)
The workaround for this is to first start installing the game on the new computer using the Epic Launcher. Let it download for a few seconds, then abort the install (don’t just pause it) from the launcher. Then go in to the folder and delete the game directory on the new computer. And then copy the files from the old computer to the new. Finally in the Epic Launcher click “Resume” and it will verify the files rather than re-download and let you play the game.
This solution is described in How to Move Fortnite to Another Folder, Drive, or PC. The problem is also discussed in EpicGamesLauncher – Recognising already installed files which includes some hints about a
C:\ProgramData directory that may contain the hidden state that’s missing if you just copy the program files. I didn’t pursue that avenue for making things work but it’s a good idea.