oh, gosh, that’s funny. We were asking the exact same question when Congress started using that ‘interoperability protocol’ term in MACRA and 21st Century Cures in 2015.
HTTP and websockets stop at layer 4 in the Open Standards Interconnect 7 layer model, whereas the specifications that have been approved as meeting the definition of ‘Interoperability Protocol’ use all 7 layers. So http/s and websockets are part of it, but not all. Data packet shape is also defined, as well as application registration. There’s also a legacy interop protocol called HL7 v2 that uses push messaging over raw TCP with defined application endpoints.
But once those things are in place, they just park the monolithic app next to the other monolithic apps.
It’s like commercial trucks and having a loading dock and parking for semi’s. If you’ve got the infrastructure, and the vehicle behaves properly, having a monolithic something isn’t a problem. But don’t try to roll your mad-max customized art-car up to a loading dock if it’s not meeting ground clearance requirements, etc.