For a start I find it telling that my comment was downvoted to -4 instantly. How can you downvote someone for stating what they do or don't find natural in their own language? Do you think I'm lying? Maybe I should start making comments about what I find natural in French instead?
You've all given examples of contexts where you don't find it unnatural. I agree with s some of them, so let me correct my original comment: it doesn't always sound natural.
> "I interviewed a developer yesterday." "Were they any good?"
This sounds OK if the gender has not yet been mentioned, but as soon as it has been mentioned it would be unnatural to use "they".
> Do they have grey hair? Yes, they do.
Also OK, until the gender has been established, as above.
> "Fin updated their profile picture"
This sounds completely unnatural to me and yes, I have noticed it. This is the same usage as in the PR in question here.
I also find it unnatural when "they" is used as the subject of a sentence in singular, like "When they travelled to London, they drank tea". If that's a single person, it sounds really jarring.
I think it's probably to do with the verb conjugation rather than the pronoun. As a French speaker you probably understand that the verb is equally, if not more, important than the pronoun. In Spanish they don't even bother with pronouns, it's all about about the verb. Unfortunately "they is" sounds totally wrong to every native speaker, so you're stuck with "they are", which is used for plural.