Two photos released by the White House were said to show him working at Walter Reed hospital, where he went after being diagnosed with Covid. It was soon noted, however, that a) he was merely writing his own name on a piece of paper, b) the two shots included the same props despite being taken in two different rooms, and c) the two shots were taken minutes apart … despite being taken in two different rooms.
The EXIF data embedded in the photos revealed that the photos were taken moments apart.
There's some argument over what he's actually writing with a sharpie on a blank sheet of paper. I used photoshop's "distort" tool to crudely fix the perspective on the paper and it corresponds with his signature exactly.
I think it's important to note that this sort of casual, blatant lying is normal with the Trump administration. It doesn't represent a specific effort to conceal the severity of his present condition beyond the usual level of bullshit about everything.