Aitchus: On Reddit the "Verified GOG Rep" said this:
[...]
From the same thread:
A user asked:
"In description I can read that I can install game with GOG Galaxy app.
Does this mean that I can install and launch games from Epic without Epic Launcher?"
With the following reply:
"[–]-chandra-Verified GOG Rep[S] 1 point 4 hours ago
No, the launcher is still necessary as these games have DRM. It means that, if you already have the Epic launcher installed, you can install the game without leaving the GOG GALAXY app. Otherwise when you were to install the game, it will ask you to install the launcher."
(emphasis mine)