"So is not agreeing on facts/truth The Great Filter?"

It's a possibility I've considered before. To put some math meat on the idea, consider that as education increases, the number of thoughts you can conceivably think goes up exponentially, but your ability to discriminate probably goes up only polynomially, and possibly as badly as somewhere around linearly. So the smarter you get, the more bad and wrong idea come within your reach, and the less resources you have proportionally to disprove each one. And this is assuming a very idealized situation in which you are a perfectly rational observer attempting to dispassionately filter truth from untruth; any deviations from purely rational make it even worse. Note there's no reference to "humanity" in there; it's a problem everyone in this universe will have. (It's basically a restatement of the impossibility of Solomonoff induction.)

As an example of what I mean, consider the claim "the quadratic equation is x = (-b +/- Sqrt(b^2 - 4bc)) / 2a". My children are still too young to have any clue what that means. It requires substantial education to even begin to think this wrong thought, or any of the many related surrounding wrong thoughts; there's who knows how many ways I can mutate the right answer to be just slightly wrong, to say nothing of simply making something up. All of these wrong possibilities are available to you, once you are educated.

On the one hand, I use math here because it allows me to give you a clear example of an unambiguously wrong thought, on the other hand, it also betrays me for the very reason that it is unambiguously wrong. Math gives us tools to raise our confidence in the true quadratic equation even above the exponential noise of possible wrong answers. But the real world has much bigger problems than that where we lack such tools; how shall we structure our society to obtain a given goal? How shall we even determine what those goals are? How can we be sure that we are not actually putting ourselves on the path to inevitable destruction, even with possibly every participant trying to avoid that in all earnestness?

You probably just had some sort of thing leap into your head, perhaps about the environment or war or social inequality or something... how can you prove that you are not in fact 100% wrong? What if the only way we can still be alive in 10,000 years is precisely that we must unambiguously destroy our environment in order to be forced to learn to deal with it, because it's going to happen anyhow later (supervolcano, asteroid, etc.), so better to learn to deal with it in slow motion? What if space is empty because all the other species did learn to live in "harmony" with their environment, until it blew up and they couldn't deal with it? What if war is a necessary component of survival because without such evolutionary pressures, intelligent species inevitably just fade out of existence as intelligence is selected away, Idiocracy-style? What if the only way for anyone to survive the next 10,000 years is to create a rich upper class that at some point will be the only ones to survive some inflection point crisis? (What if the only way through the Singularity is for some rich person or set of people to be the one powerful enough to hold back the first rampaging AI, so all the egalitarian species keeled over dead because the AI trivially economically overpowered any given individual before extinguishing its own spark?) I'm not "seriously" proposing these ideas, but when it really gets down to it... you don't know. Neither do I.