Evidence of well-known companies and organisations accepting and offering Mx as a gender-inclusive title.
Extract from Document
Mx has been around since at least 1977 as a standard title without gender connotations, though its use didn't take off until around 2000. It can be used by anyone regardless of gender or marital status. It follows the M* pattern: Mr, Ms, Mx. It doesn't require a qualification or career as Dr and Rev do. The x represents a wildcard character that removes gender. It's pronounced similarly to Ms: Mux or Mix.