Proton-GE includes media libraries that valve can't include, which fixes video playback in many older games. Valve has found a different way to bypass this issu

Proton-GE includes media libraries that valve can't include, which fixes video playback in many older games. Valve has found a different way to bypass this issue, by sharing video content through their shader distribution system, but that may not work for all titles. Proton-GE also supports more experimental features long before they get added to regular proton, and includes various hotfixes for games that won't work under normal proton. Usually the recommendation I make to people playing on linux is to try with regular proton or proton experimental first, but if that doesn't work then try the newest proton-GE instead.