Wasn't Omar part of the mujahideen?
Descent into Chaos: The United States & the Failure of Nation Building in Pakistan, Afghanistan & Central Asia and In the Graveyard of Empires: America's War in Afghanistan are also great reads about Afghanistan.
Not as on topic, but still good would include The Way of the Knife: The CIA, a Secret Army, and a War at the Ends of the Earth about how the CIA shifted towards more targeting operations and the military shifted to more intelligence gathering and how that has blurred the lines between the two. And The Accidental Guerrilla: Fighting Small Wars in the Midst of a Big One about how insurgencies work, how local people are recruited and coopted by globally minded jihadists using local problems, and how a counter insurgency operation requires understanding and addressing local dynamics and issues, and breaking the connection between locally focused fighters and global jihadists.
But the ISI was not run by the CIA. Pakistan had, and still has, their own agenda and priorities that do not align with the US. So if you are implying that the ISI funding of the Taliban must have actually been the CIA, that is not supported by the evidence.
None of that is to say the CIA misadventures in Afghanistan before 9/11 were somehow harmless. They handed over briefcases of cash to Jalaluddin Haqqani, who became a key ally of the Taliban and the Haqqani Network he created ended up supplying explosives to the Taliban and lauching highly successful suicide attacks on US forces in Afghanistan.
I know people like simple narratives and having someone to blame, but the situation in Afghanistan over the past 40 years is not simple and is not because of the actions of just one country.
I never made such claims; starting on an ad hominem and ending on a strawman doesn’t really lend much credibility to what lies in between.
Pakistani ISI backed Gulbuddin Hekmatyar, the “Butcher of Kabul”, in an effort to help install a Pakistani friendly government in Afghanistan, but backed off after pressure from the US. The Taliban was then formed in southern Afghanistan by Mullah Mohammad Omar, also from former Soviet fighters, and quickly conquered significant territory from the other warring factions. The Pakistani ISI backed them, but covertly to avoid pushback from the US. The Haqqanis and Gulbuddin Hekmatyar became allies, with the Taliban controlling the majority of Afghanistan, while Ahmad Shah Massoud and his “Northern Alliance” controlled the north.
The US under Clinton was pretty wishy washy about Afghanistan at that point, mostly just wanting the fighting to end. But they did work with Massoud and the Northern Alliance in order to attempt to target Osama Bin Laden after the 1998 embassy bombings. Under Bush, the CIA was in the process of beginning a covert operation to support the Northern Alliance against the Taliban, but then Massoud was assassinated by the Taliban on September 9th, 2001, and two days later was 9/11.