I recently translated this (männlich/weiblich/divers) in a job ad as m/f/x. Other suggestions made by colleagues were more experimental. However, I am now seeing “m/f/d” (mainly on German sites?). And in the USA there is m/f/d/v meaning masculine/feminine/disabled/veteran.
There is an academic job site in the UK and I see they have Professor (m/f/d) International Management and Finance at the Technische Hochschule Deggendorf and Postdoc (m/f/x) at the Helmholtz Centre for Environmental Research in Leipzig.