The comments about President Trump's health, both physical and mental, are concerning, and a lot of print space has been devoted to it and possible ramifications, but little to the level of reporting.
There were several presidents with hidden illnesses. Franklin D. Roosevelt had polio, and John F. Kennedy had Addison's disease. Other leaders in the U.S. and other countries have most likely either hidden or lied about frailties that would have kept them out of the job.7 comments on this story
Doctors are subject to rules of privileged information and cannot generally be required to divulge patient information. A permitted report could range from "in good health for their age" through "has some concerning health issues." Any release of information will need detailed notes and explanations for the majority of readers.
Even if there are medical concerns, they probably won't matter unless they are severe mental health issues. The complexities of trying to remove a "broken" leader generally requires the support of both sides of the aisle, and this is not going to happen.