Selective mutism is an anxiety disorder in which a person who is otherwise capable of speech becomes unable to speak when exposed to specific situations, specific places, or to specific people, one or multiple of which serving as triggers. Wikipedia

An anxiety disorder Wikipedia Disambiguation

Anxiety disorder causing inability to speak under certain circumstances Wikidata

A severe form of social anxiety disorder characterized by a total inability to speak or communicate orally in certain social settings. The inability to speak is involuntary and persistent, and is not caused by a communication disorder, neurodevelopmental disorder, psychotic disorder, or intellectual disability. Wiktionary

Inability to speak in certain social settings. Wiktionary (translation)