Unfortunately common issue with a lot of Epic store games, many don’t work or have issues when compared to the steam version. The protonDB reports are all 6months+ in age as well, so it’s possible something has changed with the game in that time. Found this discussion on reddit, where it sounds like it runs for most people but with terrible performance.

I know some Epic games take a really long time at first load. The Epic version of gloomhaven could take 1-2 hours to load the first time if I recall right, but after that first really long load time it would work fine. I’m assuming it’s compiling shaders or something the first time.