Is collapse of arytenoid into airway upon inhalation with strider/breathlessness in adult with normal vocal chord movement mechanical or functional?

Depends. Good question. Depends why it is happening. If it is occurring due to muscle tension dysphonia (inappropriate use of muscles of voice production), it's functional and may improve with voice therapy by a Speech a Pathologist. Other causes such as swelling or trauma are not functional, though it is not common that they are referred to as mechanical. Be sure to follow up with your ENT on this issue,