I was annoyed last time I bought flea medication from one of the big online veterinary suppliers.
The options of titles were Miss, Mrs, Mr, Dr, Mx(!) but no Ms. WTF?
I've never heard of anyone using Mx as a title for a person of unknown sex, eg to address Alex Smith as 'dear Mx Smith', I would always assume it was associated with someone who considered themselves trans.
If I had to write to Alex and did not know if Alex was male or female or his/her preferred title, I would just write 'Dear Alex', even professionally, although obviously if Alex wrote to me and used a title, I would use that in all future correspondence.
I don't see the point of titles anyway, and would rather do away with them totally, as the only purpose they seem to serve is to drag women into a mess of 'is it Miss, Mrs or Ms' with a lot of people still having negative connotations of Ms, rather than seeing it as a neutral alternative to Mr.