I think we have discussed this in the past, FM, but rather than "just forget about it" let me give you take on it.
RL brought the words “theists” and “atheists” immediately into the discussion about “reality”...so I am assuming the question of the existence or non-existence of a GOD or gods was in his mind.
In any case, a primary question of “reality” is: Is there a GOD (are there gods) or are there no gods?
I am absolutely certain no one will ever KNOW if there are NO GODS.
I am absolutely certain that IF THERE IS A GOD…it is possible to KNOW there is a GOD. For a variety of reasons, I think it highly unlikely, but IF THERE IS A GOD, it is at least possible to know. (The GOD could be a personal GOD and could reveal itself in an unambiguous way if it chose to.)
Once again, for a variety of reasons, I think it highly unlikely, but it is at least possible. For that reason, I disagreed with your statement that I am certain no one can know.