This is going to create a massive exodus of refugees, of which Europe is going to have to shoulder a much bigger burden than the US.
This predicament is the joint responsibility of Biden and Trump. It is also the responsibility of US presidents dating back to Reagan, when the mujahideen (plural of mujahid, one who wages jihad, or Islamic holy war) were cynically aided in order to undermine Soviet efforts in that country. Britain is also partly responsible, as the Thatcher government was also helping to aid the mujahideen. When the Soviets left, the Taliban arose from their ranks.
It was a hare-brained scheme hatched twenty years ago to try to convert the country into a liberal democracy, alongside blowing up the al Qaeda bases there. Ever since, the Taliban counter-insurgency has been undermined by misplaced strategic priorities and thus doomed to fail. The staggeringly corrupt puppet government ruled in the interests of the Afghan metropolitan elite only, and not in that of rural folk whose loyalty was required to counter the Taliban's influence. The pointless Iraq debacle diverted attention and resources away from the conflict at a critical phase.
The US withdrawal reflects some basic ignorance of the country and the conflict in matters as simple as the best time of the year to make a withdrawal. Biden's notification of withdrawal coincided with the start of the Afghan fighting season
Afghanistan fighting season - Wikipedia
If he had delayed the plans for several months, it could have made a world of difference to the outcome.
The Taliban's big push to capture the whole country has made them exposed and vulnerable, as they have effectively morphed into a conventional military force (with inadequate weapons and training when pitted against US forces). But this opportunity for decisive military action has been passed up as well.
It would have been much less calamitous to have thrown in the towel in the 2000s, rather than to wait until now. For twenty years, a false hope has been cultivated among a segment of the Afghan population, who are now faced with the reality of a return to Taliban rule.