New and looking for tips!!

Hi my name is Mandy and just almost 2 months ago I adopted my dog Hammy (Pit/Great Dane mix) from the shelter. I searched hours and hours and his profile was the one I kept coming back to. It even said he was good with people and able to walk by other dogs with no issue...but now it's become a huge issue. Hammy, unlike any of my other dogs I've had, needs constant socialization with other dogs. I have a little dog park on my roof of my apartment and it's hit or miss if we see someone because I work the morning shift at a news station. So for exercise we'd go on walks and he was improving each trip. Then one day I felt like he was okay to go to the REAL dog park. And he had the time of his life! So I kept taking him because he got to run and play and have fun. After about 4-5 trips to the dog park, he can no longer walk by another dog or human without losing his mind. It doesn't start off with a growl, he goes to full attention and starts barking. When I pet him and reassure him that everything's okay the bark goes to a cry - jumping, lunging, trying to get to them. He does this a lot with dogs that don't stop and play with him. He's a big guy and it's terrifying for others to see him lunge and bark his head off while they're just trying to go on with their day. Even if people stop at him he'll sniff their hands and then start barking again.

He's a sweet beautiful boy and a staff favorite at the shelter but I just have no idea what to do here. I feel like the more socialization I give him the more he declines in his training and his abilities to even just walk by someone.

I'm open to tips, suggestions, etc. I've tried to find him a doggy daycare but a lot of places in my area doesn't accept his breed.

I love him with all of my being but I'm growing insane in the progress 😅