Any idea how Facebook handles people with rare gender pronouns? Doesn't Canadian law require use of chosen gender pronouns and Facebook operates in Canada.

It really doesn't, https://www.nbcnews.com/feature/nbc-out/canadian-lawmakers-p... if you want primary and secondary sources.

Basically it just says you can't actively discriminate against someone because of gender identity. Which had been the defacto law for a long time.

I think I've seen "their" used instead of "her" or "his" where people declined to specify any gender. This works in English but not in German for instance, where I think they write "ihren/seinen" which translates to "her/his".

I suppose that's as far as Facebook's support for gender choices goes.

Ah, I thought that you’re faking your interests and posts, but it’s just a gender setting.

I thought FB allowed you to set your gender and pronoun independently now?