Copy game to other PC?

Can you copy a game (Fortnite) to a USB stick and then add it to another PC without having to download the game is that a 300iq move or is not it?

Generally, this works. If the game is started via any launch and not via an .exe (I think that's the case with Fortnite), it could be a problem.

If you just copy a game, it is not automatically installed. Whether you can actually play it depends on what you have copied and what you have not (a game is rarely in a folder).

If your game is started via a launcher, you can also specify the folder where you have copied the game, installation folder and then re-download / install the game.
The launcher should recognize which files already exist and only download and install what is missing.
But even there it depends on the launcher, whether they recognize that or not.
You just have to give it a try (or find someone who has already tried it).