Keep in mind that Triplebyte profiles have no reason to exist except people looking for work, and that most people have a reason to want to be sure that a current employer does not have an easy way to find out that they're looking for work. I can have a HN account and it doesn't make anyone think I'm looking for work, but if an employer sees my profile on Triplebyte, it tells them at the very least that I was at some point looking for work. If they see it on Triplebyte after having previously not seen it, it tells them that something changed recently.
I would definitely think this should be an opt-in thing.