On a related note, as you mention, the author's husband, Zalmay Khalizad and what he knows is probably quite a story in itself. His fingerprints are all over the withdrawal agreement hence they are all over the situation as it unfolds. He is a remarkably connected person, having served in various capacities in the Bush, Obama, Trump and Biden administrations, and an ethnic Pashtun himself.
It's difficult to know whether what is happening today in Afghanistan could be any combination of the following:
1. Inevitable hence nobody's "fault" per se, assuming you agree it was right to go there in the first place
2. Trump's fault for setting up a deal that was basically a complete surrender on Taliban terms, and one that excluded the Afghan government completely thus guaranteeing their isolation and collapse (which may have been predestined anyway)
3. Khalizad's fault for possibly functioning as a Taliban representative in US Envoy clothes the whole time, and duping Trump attention span was limited and whose concern was mainly consumed with re-election optics
4. Trump's fault for public statements assuring withdrawal which basically undermined anything Khalizad was trying to negotiate since Trump was now promising the public that he was going to give the Taliban what they wanted anyway so why would they trade any concessions?
5. Biden's fault for accepting Trump's deal and then executing it as incompetently as possible.
6. Biden's fault for possibly checking out and never engaging in Afghanistan post inauguration at all
7. Biden's fault for disregarding the advice of the military and/or intelligence community and making the decisions himself
8. The fault of the Afghani people for being hopelessly directionless and completely unwilling to meaningfully resist the Taliban themselves
There are undoubtedly other possibilities. The exact combination of root causes is really not possible for an average citizen to discern. It's complicated. Deep in TLdr territory