However, in most applications and services, this is not used like that. The gender mapping seems to be used exclusively to determine whether the marketing emails should start with "mr." or "mrs.".
Die deutsche Sprache hat Geschlechter, welches Geschlecht passt am besten zu dir? Maskulin, Feminin, Neutrum oder zurück zum Englischen wechseln?I want to think we've grown out of the early design era of launching an image editor and getting asked on first run what format I want to use for exporting images. Ask me that question when I hit the export button. Similarly, ask me questions about grammar when it's relevant to the software, don't ask me questions up front that might never be relevant to my use of the software.
As an analogy, imagine if you started using Bandcamp and it asked you up-front for tax information just in case you ever decided to publish an album in the future. If the user hasn't ever switched to a language that requires knowing what gender variants they use, then that question is just one additional tiny piece of signup friction sitting in front of your service that you could get rid of for the majority of your users.
Anything vaguely social is going to have instances where you want to refer to a user in the third person.
Of course, an easy solution to this is not to ask for gender per se, but for what pronouns to use. Even a dropdown with "he/she/they" options is going to cover basically everyone. If you need something more complicated than that, so be it, but probably YAGNI.
https://www.sos.ca.gov/business-programs/diversity-boards
The simplest way to game this is to claim to be a bisexual. This is even easier if you’re already married, since no one will expect you to prove it.
Now sexual orientation, that's a head scratcher.