Can we know this is true with absolute certainty? There's a way that it can be known. If meaningful signature matches we're permitted in Pennsylvania, Georgia and Arizona the answer would be that at least the election officials believe the election was on the up and up. Absent that, they believe that the election was stolen. We have not seen these meaningful signature matches permitted in any of the crucial states.
Conclusion: the election officials and Trump voters agree that the election was stolen. This inference is so strong as to almost be
necessary. Robert Barnes makes this point poignantly in the video below at timestamp seven minutes.
Earlier in the video Barnes makes the point that the big selling feature in these election machines was that they make images of all the ballots so anybody can review them anytime they want! Great! What good does that do if you are prevented by the courts from doing so?
No one can say for certain that the election was stolen, but we have a near necessary inference that everybody agrees that it was.