From what I hear, it is a " new " social media like Twitter / X. More open and federated in nature, supporting open protocols. Looks like BlueSky has been around for a while and was invite only. They got 3 million users so far and open source channels are talking about it.
When I tried to SignUp, it asked for email ID and password, then for phone number verification.
For me, perhaps one more social media platforms is not going do much harm. Also, another place to keep informed and promote your services sound nice.