Since it has been nearly 19 years from the event, and not one person has come forward to announce an involvement by any branch of the government in planning/execution of the 9/11 attacks, one could support that with rather high certainty, that the government was not involved with planning/execution of the 9/11 attack. Notice I did not indicate a 100 % certainty.
Disprove that.
One thing that bothers me is the phrase "the government" as if it's some monolith. It's highly fractured, which is one of the reasons that 9/11 actually happened. Info was not shared. Robust firewalls and strong agency tradition prevented sharing.
Just look at the response to Covid-19. It's disjointed. This is not a bug, but a feature. Which is the problem the OP is trying to address. Even if someone in the CIA wanted the USAF to not scramble fighters, it's going to take some co-ordination at very high levels. Also, it would lead to a different inquiry. Why didn't they react? A smaller conspiracy doesn't solve problems. It creates them.