Is there a scene at the end of Sanity with kobolds? Google's AI said there is, but I can't find it.
No, there is not.
Do not use AI if you need very accurate information because most of the times the AI will say yes but referring this time the game has "Sanity endings" in your question and not specifically for you character.
Use the wiki of this game instead which as far i know it keeps updating info related to this game.
Link to the wiki for those unaware: https://lustfuldesires.miraheze.org/