I’m not sure how reliable this person is but:Miami currently has 4 DPs according to the official MLS roster page: Martinex, Pizarro, and Gregore, plus Campana as a Young DP. None of them are listed as being on loan.
That's already one more than is allowed. The 2023 MLS Roster Rules specify that each team gets 2 DPs, you can buy one more, and Young DPs have a lower budget charge but still count as one of the DP slots. Plus you cannot trade DP slots.
I don't know how Miami is having 4 DPs as it is, and then they're going to add Messi?