So All you need to do is open the Task Manager via STRG/CRTL + ALT + Delete/Entf
After you opened your Task Manager, close all Epic related processes!
And Anti-Cheat if it's still open. Now close steam, restart your pc and open, if this doesn't work, just try it again. It normally worked for every single person i know.
This is a problem with epics and with anti-cheats..same goes for Black Dessert Online.
If this doesn't work for you, than delete and reinstall Fall Guys. But it should solve all related "game doesn't work" issues.

I tried many method found online almost half day but still can't launch the game, what a shame! I just wanna refund. I dropped message to the epic/steam support but still no feedback. Quite a waste of time

Nothing you do will make the game load. The only thing you can do is try again later. You think your solution works but it doesn't, it's only because you tried again later. I wanted to play the game last night and I was "missing files", I did literally nothing and tried the game again this morning and it worked fine. No solution works except trying again later.