Delete the BenpinEX folder. I read it on a post but I can not for the life of me find it. I was having the exact problem you were and after I deleted that the game worked fine.
C: Steamfolder/steamapps/common/Valheim. Should be the top folder. Hope it helps!

same here
nvidia drivers OK
check of all the files OK
reinstall all the game OK

try to run it via run administrator. That worked for me.

Short Update. I've deleted all files in the local folder, made then check installation files. Then steam retrieves all missing files. After that, I could start.