Ice cream contains fat, sugar, and possibly toxic ingredients like chocolate or xylitol.
Cats are lactose intolerant, so ice cream may upset their stomach.
High-fat content could cause pancreatitis, and regular consumption could lead to obesity, diabetes, or heart disease.
Suggestions
It's best to avoid giving ice cream to cats altogether.
If you're determined to offer a taste, ensure it's free from toxins and only provide a tiny amount, no more than a lick or two.
Note: even if labeled as safe, any food can potentially cause allergies. When introducing a new food, please feed a small amount and observe your cat for any allergic reactions.