Are you on windows or linux, if you managed to fond the dlc files, you can most likely(not 100% sure it works with delisted) use creamAPI to make steam think you on them. On windows I’ve used CreamInstaller, which is a handy GUI that does it for you. I seem to recall I did it on my father computer running ubuntu, but don’t recall exactly how.

This is because librewolf reports itself as firefox for privacy, and vivaldi does the same thing with chrome. Their is no vivaldi string in their user agent.