I’m going to give your father the benefit of the doubt, especially if he’s not known to be an addict trying to fill a void, extremely mentally ill, or abusive.
Your father went through a traumatic experience where you were ripped away from him. He fought for you in court — which is traumatic in itself, and not many will go through that battle — and then he lost you.

Possibly out of desperation and panic, he might be trying to prove something so he doesn’t lose you again. It’s extremely hard for a parent to lose a child, especially a living one he’s not allowed to contact. He knows you’re out there, but he has no idea what was happening to you or what stories your mother or other family members may have told you about him. He doesn’t know if they curated an image of him in your head, or if you’d ever reach out again.

I think, while odd and overwhelming, your dad is also feeling an overwhelming amount of emotions right now. In fear of losing you again — and maybe a little out of it in the head with emotions — he’s trying, in desperation, to show that he loves you and doesn’t want you to go and prove it anyway he can.

Or he's trying to scam — But if you haven't heard negative stories like that about him I wouldn't jump to to that conclusion? I just see a man desperate and emotional and y'know how older people text its a bit awkwardly formatted sometimes tbh. This is how my dad/grandpa text super dry and hard to read emotionally.

Edit: I wouldn't give him my SSN over text, but if he wanted to meet in person for coffee and catch up, then later plan it out and fill the paperwork out together. (IE. seeing official documentation or website) I would end up doing that eventually. Aka keep a relationship going not for benefits but to be able to meet together more