The thing with all the arguments about NATO expansion is, it's driven by countries pushing hard to join, more than by the US or other existing members actually wanting to expand. Most of those newer members are too small and/or too poor to contribute much to the defense of NATO's older members, while expanding the responsibility and risk for the alliance as a whole. And why do they all want to join? At least in part because of the threat of Russia - part is also just because it's seen as a status boost and a sign that they 'belong'.
At no point since the fall of the Soviet Union, as far as I'm aware, has Russia faced any credible threat of attack, invasion, foreign countries wanting to claim any part of its territory (such as the parts of Finland and Germany that they took after WW2), etc. The reverse is far from true. Russian military interference outside its own borders, other than the nasty adventures of the Wagner Group (and Syria but yeah, the US or NATO hardly have clean hands in the Middle East), have generally been in defense of Russian or other allied minorities who could at least claim that their rights were being violated by their respective national governments, that's true, but those looked more like pretexts than the real reasons and they have certainly been counterproductive in actually resolving the disputes or conflicts in question.
But as for Russia asking to join NATO (a quick search mentions such a question in 2000, not sure when the other times you mention were), yeah, that could have changed things for the better for sure. Or some different way might have been found of involving them again in the security framework for Europe, the way they used to be in the 19th century.
I agree with you that the Yugoslav Wars in general were to a considerable extent civil wars with atrocities committed on all sides, with the Serbian ones given more prominence than those of the Croats, Kosovo Liberation Army and others. In a way it's understandable that as the dominant power in a multi-ethnic Yugoslavia, Serbia wanted to maintain that position and after that became impossible, that they wanted to safeguard and protect the Serbian minorities in the republics dominated by other groups, including to this day in Kosovo. But that doesn't justify their war crimes, or as the case may be their support and protection for Bosnian Serb war criminals like Karadzic and Mladic. And the various international courts supposed to deal with these war crimes have also persecuted Croatian and other leaders.
Reading now about Operation Storm specifically, I'm very much reminded of the 1948 conflict in Israel/Palestine - once you start looking at it on a granular level (I know almost nothing about Operation Storm, but have read in rather a lot of detail about the 1948 conflict, such as Benny Morris' books), you have to ask, where do you draw the line for your definition of ethnic cleansing? If in some places your troops have in fact used violence to expulse the locals from a different ethnicity, while in other places those locals fled before your troops even got there, are you guilty of ethnic cleansing for all of them or only for the villages where real violence was used? And what difference does it make if at least some leaders of the community in question are suggesting that it is in fact better to evacuate?
At a minimum, I'd indeed have to conclude that if 'the Nakba' as a whole is considered ethnic cleansing, then so too is Operation Storm.
And yeah, as for the NATO bombing of Serbia, it does look like it was both done on questionable grounds and moreover, at least in the short term, actually exacerbated the Serbian violence against Kosovars that it was supposed to stop. Though given the small number of civilian casualties, 'merciless bombing of an entire nation' does seem over the top.
I found a detailed report to Congress from the Special Inspector General for Afghan Reconstruction, see link. The specific passage dealing with your point about air support is on pages 10-11. And it makes it pretty clear that, yes, the drastic drop in American air strikes made a big difference in emboldening the Taliban - but that drastic drop happened immediately after the Trump administration's Doha deal with the Taliban in February 2020. Not due to any decision by Biden. US generals immediately changed their decision making about airstrikes and reduced them by something like 90 percent compared to the preceding year - and Trump did nothing to change that in the remaining ten months of his presidency (not that he really could have without immediately blowing up the deal his negotiators just signed, and not that I think he actually had much to do with said deal or with thoughtful policy making about Afghanistan).
The rest of the report also makes pretty clear that the demoralization and degrading of the Afghan army started right then and there in Feb 2020 - though for a long time President Ghani didn't really believe that the Americans were serious about withdrawal, especially after the change of president, so in that regard Biden's reconfirmation in April 2021 that actually yes, it was really going to happen, did deliver a further blow.
So yeah - while of course there's going to be minor aspects on which I'm sure the Biden administration could have done better, the same would've been true if the withdrawal had happened under a Trump administration and I'm feeling pretty confident about my position that for the most part, the collapse would always have happened much like this, with only quite minor differences depending on who happened to be president.
Not sure if you misunderstood me or just didn't feel like engaging with my point, so I'll repeat it just in case: I was talking about the huge numbers of illegal immigrants in the US, people who are already made it across the border and are living and working in the US, who voluntarily leave again, because they've made enough money or because their family back home needs them, or some other reason. And then very possibly come back to try again years later. That's quite different from Europe with all its refugees of whom very few can or want to ever return, not unless somehow Assad or the Taliban get overthrown which doesn't look remotely likely.
I also don't think that either European or American asylum policies should be based on what some clueless student protesters have to say, thank you very much. You have to draw the line somewhere of course, can't just let in absolutely everyone who'd rather live here than in their own country, but I don't imagine you and I will quite agree on precisely where to draw it, so agree to disagree.