So, random, but my cured vampire Sim is suddenly able to eat human food without throwing up!
Idk if it's related to the patch that was just released, or if it's because I just moved him into a new household, but I accidentally left food out and he went and got a plate (salad) while I wasn't paying attention but he didn't get sick! So to test it, I had him make breakfast in the morning (eggs) and he got a happy moodlet from the tasty food!
Advice for testing: if you can, try moving your affected Sim into a new household. In my case, my Sim married a previously unplayed non-vampire Sim, and merged into her household before moving to a new lot. It was a little over a Sim week before I let him eat normal food by accident, but I was pretty diligent about keeping him well fed on harvestables. Good luck!
***UPDATE: false alarm, he's throwing up every time he eats now. Everything was fine until he had the ham dinner (excellent quality) for the Christmas event. That made him sick, and now everything, including foods that were fine yesterday, is also making him sick. Back on the raw diet I guess.
The only differendi, besides the fact that it was a 'grand meal' is that there WERE other Vampires present when he ate the ham dinner and got sick. Subsequently, he's been alone while eating and is still getting sick. 🤷