I had a tiny problem, I had just switched to Linux and installed Steam. I wasn't able to run the game, however, no matter how many proton versions I tried or wtvr. Then I ran steam from the terminal with the following command:

$ STEAM_DEBUG=1 steam

I didn't install Elden Ring on my OS's disk, I installed it on my HardDrive, that was a NTFS partition, so this was always showing up on the terminal: $ '/mnt/sda2/SteamLibrary/steamapps/compatdata/1245620/pfx' is not owned by you

Turns out, I had to change my disk's partition to Ext4 (cause Proton expects this type of partition and not NTFS), and after reinstalling Elden Ring on that same partition it worked flawlessly without any tinkering! I'm so glad to where Linux has gotten :)