Dear Pante, I am seeking to understand the state of mind of an arhat.
Is it a state of knowing everything about reality, or can a subset about reality that could vary from person to person?
What would be the lowest common denominator?
An Arahant is not someone who knows everything.
A fully enlightened Buddha is someone who has unobstructed knowledge.
So it's kind of like knowing everything, except it's knowing whatever you want to know.
So apparently the Buddha was able to find an answer to every question that he posed, every question that was posed to him.
Any knowledge that was required, there was an unobstructed access to it.
But for an arahant, that's not the case.
In fact, a better point is that no one can know everything, because knowing everything implies knowing two things at once.
You can never know more than one thing.
But the Buddha had unobstructed knowledge.
An Arahant only knows four things and that's the Four Noble Truths.
They have the realization of the Four Noble Truths.
More importantly, they know enough to free themselves from suffering.
An Arahant has to let go of everything.
Only a Buddha has to know everything.