What we call reality exists.
Regardless of us being able to faithfully express whatever we know about it.
Regardless of how much of what we know we are willing to share with others.
Regardless of some of us using their knowledge to impose themselves upon the less knowledgeable.

The irrefutable proof about reality being a fact is not that we have chosen to call it so. Or even to call it at all.

The irrefutable proof that reality is factual is, duh, another fact.
That nobody, no matter how knowledgeable, powerful or both at the same time, has ever been able to impose their will upon the said reality for any significant length of time.

No dictator has ever been able to consistently subdue a people. To kill it, yes. To consistently subdue it, NO. Lately, most of them have also lost an erstwhile relatively common ability… that of bequeathing their power to their intended successor.
No scientist has ever been able to pretend they really knew what they were talking about. No genuine scientist, that is… That they have a clue… yes. Of course!
A fair understanding of what’s going on… that is increasingly plausible.

That at least one of the above possesses the ultimate knowledge/power about even the minutest portion of reality…