From ActuallyAutistic Wiki

Allism is the antonym of autism. An allistic person is someone who is not autistic.

Neurotypical (or NT for short) is often used synonymously with allistic by many people. However, this is incorrect: while an allistic person can, by definition, never be autistic they can still be neurodivergent in other ways. (For example: someone who isn't autistic but is ADHD is both allistic and neurodivergent)