Those planes do fly without the [president] sometimes. Could be maintenance related, training flight, whatever.
I tend to think most of the so called clones or doubles are not. Reason is I've spent most of my career working with digital images, and usually the 'proof' people talk about is related to pixel artifacts or lighting.
That said, I think the mind is very powerful. Dress up a lady who looks almost like Hilary in Hilary's clothes, and blamo….on camera people will assume she is Hilary. Anyone wearing a mask, just makes it that much easier. Most likely scenario with Biden IMO is there could be more than one look-alike for opportunity photos and casual appearances, but they would use the original for up close speeches with a mike and camera.