Loyalty: The only two options in the title field on a Miles & More profile are Mr. and Ms. (The options appear when creating a profile; I’m unable to find a way to view or change the title after creation.) There is an optional secondary field for “academic title” that includes Prof. and Dr. options, but a binary title must be selected.
Booking: The only options in the title field when booking a flight are Mr, Ms, and variants with Prof and/or Dr appended.
Check-in: I have not yet attempted check-in with a gender X passport on Lufthansa.
Let Me X Plane 