Is Mx. the default title for Male non-phd holders?
Mx is a gender-neutral honorific.  It's probably not a typo.

Dr would typically be used if you have a doctoral degree, and Prof if you are employed in a professor-like capacity (it means different things in different countries, but generally any semi-permanent faculty job is reasonably included).  Otherwise, you can decide which of Ms and Mx fits you better.

If you feel that there isn't an option that's appropriate for you, you can take it up with the journal.