This is an unfair thing about war: victory is claimed by all, failure to one alone.
NATO losses, 3,502 have been overwhelmingly US-side(2400), with Canada (157) and UK (456) suffering the bulk of the rest. Not coincidentally, Canada and the UK did a lot of the fighting alongside the US initially, but withdrew in the past. Losses, which corrected for Canada and the UK's population, were quite comparable to US sacrifices.
The rest of the NATO missions left in 2021 were not in fact a deterrent to the Taliban, as was probably predictable in advance. They have neither the airpower nor the airlift capability to project a large force semi-permanently in Afghanistan. And European public opinion would most likely not have supported such a mission if it involved extensive combat.
The ANA should have held, maybe. But as it didn't, without the US, the country collapsed.
Many are upset at the takeover by the Taliban, from women's groups to Europeans, to Americans. To, of course, the Afghanistan. And NATO+US veterans too, but they did sacrifice, so they certainly have a say.
From the linked article:
German politician Armin Laschet, the heir-apparent to outgoing German Chancellor Angela Merkel, described the situation even more harshly.
“This is the greatest debacle that NATO has seen since its foundation, and it is an epochal change that we are facing,” he said this week.
Seems pre-positioning for an election campaign is a time for strong language.
It is very regrettable that the Taliban have taken over, but the people doing the regretting expected the US to foot the bill for the foreseeable future, with no exit in sight.
One can certainly argue that the US had obligation towards the Afghanis. However, had the US not invaded - entirely at its own initiative and for its own reasons - in 2001, those same Taliban would have remained in power. After the Soviets' whipping, it was clear that as much as the world was aghast at Taliban behavior up to 2001, no one was going to intervene militarily. Not until 9/11.
There is a lot of soul-searching to be done, certainly. By the successive American administrations (the military did its bit), most of all. By the Afghanis? Perhaps, considering ANA's collapse, except it would be blaming the victims of what's likely going to be a bloody Taliban mess in the future. But for NATO to absolve itself of any blame goes right back to the Tacitus quote above.
As to the greatest NATO challenge?
Article 6 1
For the purpose of Article 5, an armed attack on one or more of the Parties is deemed to include an armed attack:
on the territory of any of the Parties in Europe or North America, on the Algerian Departments of France 2, on the territory of Turkey or on the Islands under the jurisdiction of any of the Parties in the North Atlantic area north of the Tropic of Cancer;
on the forces, vessels, or aircraft of any of the Parties, when in or over these territories or any other area in Europe in which occupation forces of any of the Parties were stationed on the date when the Treaty entered into force or the Mediterranean Sea or the North Atlantic area north of the Tropic of Cancer.
Is Afghanistan in any of these? No. Will it embolden challengers like China and Russia? Perhaps. But, much like Vietnam before, a massive long term commitment of US forces in an area of secondary concern does not happen in a vacuum - US troop and equipment readiness is weakened in its capability to resist its likely peer enemies. It is far from certain Russia and China would not have preferred a continued drain on US resources, even if they will benefit from a loss of US prestige, confidence and influence.
And you can, of course, intra-American fingerpointing. Reps will blame Biden. Dems will blame Trump. Bush's decision to go after Iraq without finishing Afghanistan will, deservedly, get scrutinized. But perhaps the greatest blame is to be put on the US congressfolk that, right after the Afghanis kicked out the Russians in 1992, decided not to fund any relief for their formerly useful allies.
Last, if this debacle motivated non-US NATO members to fund their defense to the agreed-upon 2%? One can certainly hope.
(image copied from the above link)