I’m interested in trying out FiveM, but I would also still like to be able to play GTA Online while I still have it installed, so I’m wondering if downloading this will effect my base game in any way and prevent me from playing standard GTA Online safely.
From the main FiveM page:
Nope! FiveM does not interact with the Rockstar Online Services other than to validate your game copy the first time you launch it. This validation emulates the game’s interaction, and can not be detected by Rockstar.
It also doesn’t modify your game files at all, even when downloading server assets, so you don’t have to do anything to move between FiveM or GTA:O.