However, at this point, there doesn’t seem to be a consistent DRM policy on the Epic Store. Of the three games we've tested - Fortnite, Subnautica and the Jackbox Collection - each one seems to play by its own rules.
The Jackbox Collection seems to be DRM-free, and can run irrespective of whether you have the Epic Store open or not.
Subnautica is DRM-tied to the Epic Store, though we did find a neat workaround should you want to run it without the Epic Store (directly through the executable, say, or through Steam as a ‘non-Steam game’.).
Just right-click Subnautica’s ‘exe’ file or entry in your Steam library, click Properties, then in the Target box enter "-EpicPortal" after the game’s directory. This will connect through the game through the Epic Portal without requiring the Epic app.
Fortnite, meanwhile, has the tightest DRM of the games we tested. It doesn’t allow the "-EpicPortal" workaround, and requires the Epic Launcher to be open in the background when you play.
https://www.techradar.com/news/epic-games-store-vs-steam-battle-of-the-online-stores