OP's home instance is hexbear, which asks users pronouns on signup and automatically adds them to your display name. Admins added it to stop accidental misgendering that comes with a lot of online people defaulting to he/him and to prevent singling out trans users with pronoun tags since it's required for everyone
there's like a 25 character limit (i think. it's 20 by default but it's changeable per instance by the admins) so if your name is short enough you can put it there.
It's a hexbear feature, our brilliant mods added it like 3 years ago to stop accidental misgendering (the options also include loads of neopronouns too and the mods add to the list on request). This kicked off a struggle session where a load of transphobes complained about it so we banned them all and now hexbear is basically a trans and queer stronghold