1. Go to the game's files (steamapps/common/ELDEN RING/Game)

2. Rename "start_protected_game.exe" to "start_protected_game.exe_original"

3. Make a copy of "eldenring.exe"

4. Rename the copy of "eldenring.exe" to "start_protected_game.exe"

5. Run the game through steam

Other fixes to try first if you want to keep multiplayer but the game still wont start:

Uninstall Epic Games Launcher (Seriously, this works because EAC interferes with it somehow)

Update Graphics Drivers (For NVIDIA its Game Ready 511.79)

Verify File Integrity on steam (Most likely won't help)

Running the game in borderless windowed or windowed on startup

If nothing else works for you I would consider a refund until an actual fix comes out

My game went from not booting to a solid 55-60 FPS experience on medium with minimal stutters so far.

(NVIDIA GeForce GTX 1660 Ti
Intel Core i5-10300H CPU @ 2.50GHz
16.0 GB Installed RAM
Windows 10 Home Version 21H2)