The problem isn't the DLC; it's as I said, after the update the demo changed, and the scenes that were previously in the game simply don't appear anymore. I even clicked that I'm of legal age when that option appears on the initial screen, but nothing changes.
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If the scenes are not appearing even after enabling the correct settings, then it means there is something wrong with the DLC. Choosing the 18+ option at the start does not impact the DLC in any way.
Again, as Vin has said, if you need further help with troubleshooting, please leave a comment on the DLC's page, and I can try to assist you further.