Ah shit, yes, that's a good point. It eill give a semi random I'd to non-steam games. I don't know if the prefix is guessible, so when I need to I check each folder for it.
Now thinking though that's a fairly dumb way of doing it. I'd suggest instead searching for "EldenRing" in the .local/share/Steam/steamapps folder. May that be in your normal file manager such as plasmas dolphin, or with the find command in terminal