When the 9/11 report came out several people (not conspiracy theorists) had legitimate questions regarding why we're bombing Afghanistan when Saudi Arabia had significantly stronger links to the events than Afghanistan did.
For example most of the money, most of the people, and many of the organisations were Saudi based, and while Afghanistan's now famed "training camps" did exist, a vast majority were in Pakistan.
Even Osama bin Laden (who's a Saudi national, by the way) initially denied the attack until after the US "credited" him by name (and then he just went with it). You can find videos of him denying responsibility on YT (and later accepting responsibility).
I'm not seriously suggesting we should have bombed Saudi Arabia, that's bonkers, I am just saying that it seems like Saudi Arabian national's punched the US in the face while Pakistan distracted, and the US then turned around and beat up Afghanistan in "revenge."
The 9/11 is pretty lacking in on crete information. I'd love to hear what historians think of it in retrospect in twenty or more years, when all the dust has settled. It raises more questions than it answers (not in the "false flag!!!" sense, but in the "so who was actually behind this???" sense).
Honestly a much more believable conspiracy theory is that reputed Saudis funded it and the US and Saudi Arabia covered it up to save face while Saudi cleaned house quietly. That's totally believable and in-line with the 9/11 report, leaks, and other information.