The Taliban has never been about attacking other countries, let alone the United States. It wants to control its own country and establish its version of Sharia law. It is enemies with ISIS-KP. Al Qaeda is its own entity, and while the Taliban may play nice with them, their agendas are different. The Taliban is not out for revenge but it will fight to protect its new government -- there, not here. As for whether they will allow al-Qaeda to rebuild training camps within its borders, that would happen with or without the Taliban. There are always going to be minor militant groups in Afghanistan.

The problem for Biden is that he has gone on record with ABC News among others and said he has no recollection of his military advisors disagreeing with his plan to withdraw troops from Afganistan:

In an interview with ABC News during the withdrawal, Biden maintained that he had no recollection that his military advisers had called for keeping troops in Afghanistan:

...GEORGE STEPHANOPOULOS: They didn’t tell you that they wanted troops to stay?
BIDEN: No. Not at — not in terms of whether we were going to get out in a time frame all troops. They didn’t argue against that.
STEPHANOPOULOS: So your military advisers did not tell you, “No, we should just keep 2,500 troops. It’s been a stable situation for the last several years. We can do that. We can continue to do that?"
BIDEN: No. No one said that to me that I can recall. (my emphasis)

Also testifying were Defense Secretary Lloyd J. Austin III and Gen. Kenneth F. McKenzie, Jr., the head of the military’s Central Command.

Both men, along with General Milley, were said to have advised Mr. Biden not to withdraw all troops. During the hearing, Generals Milley and McKenzie confirmed that.

As to why the military failed to anticipate the strike by ISIS at the Kabul Airport that killed 13 U.S. servicepersons:

“We need to consider some uncomfortable truths: that we did not fully comprehend the depth of corruption and poor leadership in their senior ranks, that we didn’t grasp the damaging effect of frequent and unexplained rotations by President Ghani of his commanders, that we did not anticipate the snowball effect caused by the deals that the Taliban commanders struck with local leaders,” Mr. Austin said, referring to Ashraf Ghani, the former president of Afghanistan who fled the country as the Taliban took control.

“We failed to fully grasp that there was only so much for which — and for whom — many of the Afghan forces would fight,” Mr. Austin said.

On Gen. Milley's phone call to China before the elections, he testified:

He [Milley] said he made an Oct. 30 call to his Chinese counterpart, just before the November presidential elections, because there was “intelligence which caused us to believe the Chinese were worried about an attack on them by the United States.” He added that senior U.S. officials, including Mark Esper, the secretary of defense at the time, and Mike Pompeo, then the secretary of state, were aware of the calls.

Austin defended Biden's decision to close Bagram:

“Retaining Bagram would have required putting as many as 5,000 U.S. troops in harm’s way, just to operate and defend it,” Mr. Austin told the Senate Armed Services Committee in the first of two days of congressional hearings on Afghanistan. “And it would have contributed little to the mission that we had been assigned: that was to protect and defend our embassy some 30 miles away.”

That is a no-brainer. Bagram created terrorists and hatred of the US by its deplorable conditions and treatment of detainees.

Milley did acknowledge the danger in keeping troops in Afghanistan past September 1, the deadline set by the Taliban:

“On the 1st of September we were going to go back to war again with the Taliban,” he said. “That would have resulted in significant casualties on the U.S. side and would have put American citizens still on the ground there at significant risk.”

So why did he tell Biden he thought the U.S. should keep some troops there after that date?

Donald Trump was also criticized for his Doha deal with the Taliban in 2020.

Both Austin and Milley cast the deal as largely a failure, particularly when the Afghan military — which the United States had tried to prop up for 20 years — quickly collapsed and allowed the Taliban to take control. “We need to consider some uncomfortable truths … [including] that the Doha agreement itself had a demoralizing effect on Afghan soldiers,” Austin said.

Again, as to ISIS-KP using Afghanistan as a launchpad for external attacks, I don't think it's affected by U.S. withdrawal. ISIS-KP has been training and carrying out small attacks against the Taliban and the U.S. in Afghanistan since its formation in 2016.

ISIS is also creating havoc within Africa and Southeast Asia. Anyone who thought ISIS was crushed forever was fooling themselves. It just went underground. Every week its newsletter in Arabic publishes the latest strikes the group has made. Today they issued a special announcement that they killed three and wounded two in an attack against the Taliban in Kunar. The Wall St Journal reported more attacks by ISIS-KP against the Taliban this week. (free link).

The decision to leave Afganistan was the correct one. I just wish it had been made years earlier, or better yet, that we had never gone there in the first place.