Is it true that the moon does not exist if nobody is looking at it? I am okay with the following statements you make.
Definition of "prove" - Demonstrate the truth or existence of (something) by evidence or argument.
Proposition - The existence of physical phenomena can not be proven without physical evidence, i.e. argument in the absence of evidence is not good enough.
Definition of "evidence" - Facts or information indicating whether a belief or proposition is true or valid.
Proposition - Physical facts and information are only obtainable by direct or indirect perception. — T Clark
I don't I agree with the "Assumption- we cannot perceive the moon directly or indirectly" Maybe I am not understanding you. Please give an example. I am of the opinion that an individual can perceive the moon directly and indirectly.
I am also not sure if Bohr meant indirect observation as well. If I were forced to guess I would bet he was thinking in terms of Schrodinger's Cat as in making a direct observation as to whether the cat is alive or dead which cannot be done unless you make a direct observation That is why I used the word "directly".
Proof for the existence of the moon.
1. The moon's tides are an excellent indirect measurement that can be reliably made to confirm the existence of the moon. That was the first thing that came to mind.
2. I can use astronomical charts and computations to predict where in the sky the moon will be. I can then go outside and look up at the sky and confirm that the location of the moon matches the charts and computations. We can use mathematical models to predict the position of the moon.
3. We physically had astronauts land on the moon and take pictures of the earth from the moon. The astronauts photographed the moon as well. Millions of people all agree that evidence is real and valid.
4. The astronauts also brought back hard physical evidence in the form of moon rocks.
I see a lot of hard evidence that proves the existence of the moon. I believe that we recognize and perceive evidence of reality via our consciousness. So reality is not not defined by our consciousness it is only recognized using the tools of our senses and the mind. I cannot think of any evidence that supports Bohr's idea that the moon cannot be proved or disproved.