I think it’d be helpful to be able to have additional social links on a profile. For example, we might want to link to our Twitch, Facebook, Instagram or to a Fediverse (Mastodon, Pleroma, etc.) account.

That's been requested a few times before. For the time being, simply add any links you need into your profile description.

I second this suggestion. Given the trashfire that twitter has turned into, it cannot remain the only social link on itchio profiles. Please add Mastodon and perhaps others, as suggested above. Ideally make it so you can fill in the blank yourself with custom links, just adding a title and URL.