This issue has already occurred for other players. It's possible that you played the game before purchasing it on Itch.io, in a version that doesn't have the extra features. Since extra feature variables persist across versions (and the next version, which will be released soon, will include new settings to reset this variable), the game currently thinks your version is not an 'extra' one.

The easiest solution would be to delete the persistent save file here:

c:>users>your username>AppData>Roaming>Renpy>TheLastOasisBeforeChastity. Look for a persistent file and delete it (it's even better to delete all the saves if it's not too inconvenient for you).

(If you don't see the AppData folder, enable the display of hidden folders in Windows settings.)

Until now, there was a button to delete all saves in the game menu, but the coder removed it because it wasn't used much. I'll ask him to put it back for the next version.

Let me know if that's work.