I live in Florida and have for the past 10 years
I just found out I owe NJ 90 hours of community service from 1996
Will Florida allow me to do it here and get it over with if NJ agrees or do they not get involved in something like that?

Talk with your (or a) PO about this. Usually something can be worked out.

That is something the court and/or PO will have to agree to. Normally the local courts have agreements with specific non profit or require certain work.

So you will first have to address that it is all needed, if it is still even open. If it was not done, normally they violate that agreement and send it back to the court for punishment

How did you hear you owe community service from years ago? Generally you or a lawyer will have to appear before a judge and get it straightened out. They usually issue a warrant for probation violations.