They know the truth, but not entirely.

To state such a claim means that you yourself know the absolute truth already. ;)

The example u brought here, if true, is an example of a false negative and not of a false positive so it is not like u showed that they are liars.

Did you watch the video? I think you probably didn't, based on your comment here.

What they tell are facts in the most exact manner they know.

Definition of 'fact':

A fact is a statement that is consistent with reality or can be proven with evidence.

As evidenced in the video, there are numerous aspects here which totally contradict the alleged facts that academics typically spew out - which can quite easily be shown to demonstrate that either these academics have done no real research, have very low intelligence or are covering up the truth.

You can also discredit quantum mechanics and general relativity for failing to describe reality under certain extreme conditions, but they are still the most exact ways to model reality known to date.

Again, you appear to be stating that you have spoken with or understand the learning of every human that ever lived - how else can you make such a statement that includes an absolute statement of fact regarding the limits of human knowledge 'to date'? I can show you numerous sources of information which are not commonly known about which vastly expand on the mainstream perception. Anyone who states that 'we' know this or that, as if they speak on behalf of all humanity, is missing something quite significant in their use of logic.

Do u think there is any agenda or conspiracy or corruption involved?

I know with 100% certainty that there is - however, it is not always done consciously. Many of those involved are just not very deep thinkers and thus never notice that they are helping deny reality. Others know much more and are deliberately hiding the truth.