To be honest, you are able to use one for both as fivem is seperate. But if you want to use two separate copies, then yes you can. I would recommend just having 2 copies of steam as it's a lot more common that people mod on the steam version (unless you know how to mod on epic games). So basically, if you want to use one copy for LSPDFR for example, then just have the main folder named " Grand Theft Auto V " and just deactivate the other copy by calling it something like " Grand Theft Auto VV ". And when you want to play on the other copy just do the same thing the other way round. If you have any more questions please ask.))