Cerner isn't an EHR, it's an EMR. EHR == Electronic Health Record. Your FitBit data is an Electronic Health Record. EMR == Electronic Medical Record. Your doctor's records, how much blood thinner that nurse is supposed to give grandpa, and whether or not he's a fall risk are things you'd put in an EMR.
You can't just vibecode your way to replacing an EMR. Cerner Millennium has a shrinking, but substantial, footprint at healthcare systems across the country and around the globe. There are 25+ years of bugfixes, caveats, architecture, and other pieces of knowledge to be tracked and accounted for, and you must do so, because if you don't, people under the care of doctors could die.
It's also worth noting that the DoD uses Millennium for active service members, and I think they also use it for TriCare. American taxpayers are on the hook for dealing with the problems that Oracle's cost cuts will produce.