It seems "disabled/disability" is the safer choice.

If you search "mentally handicapped", you see that, according to "Oxford Languages", this expression is "offensive/dated".  However, Merriam-Webster says "handicapped" means "having a mental or physical disability."  Also, "handicapped parking" is still ok.  

Anyway, if you have to choose between the two, "disabled" is safer because "In the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), the APA replaced “mental retardation” with “intellectual disability (intellectual developmental disorder).” [4] The APA included the parenthetical name “(intellectual developmental disorder)” to indicate that the diagnosed deficits in cognitive capacity begin in the developmental period. The authors of the DSM-5 explain that these revisions bring the DSM-5 into alignment with terminology used by the World Health Organization's (WHO) International Classification of Diseases, other professional disciplines and organizations, such as the American Association on Intellectual and Developmental Disabilities, and the U.S. Department of Education."

This PC business is really bs, isn't it?!