So is there an element of doubt as to whether the earth is flat?
An excellent example!
Put a ball on the ground and it will stay still!
To the inhabitants at the time this was "proof" that the earth was flat
Then someone proved mathematically that it wasn't - some believed this and some didn't but neither could unequivocally "prove" the earth was round or flat.
This is where many debates are at present
Then the astronauts flew into the dark regions of space and "proved" the earth wasn't flat.
Now we know unequivocally that the earth is a sphere and the flat earth theorists are wrong given the new proof.
.. and everyone lived happily ever after!
Until someone came along with a theory that the whole space race wasin fact a hoax perpetrated to draw attention from other political and financial issues. This then casts doubt on the proof that the Earth is round - so there is some doubt!