Inevitable because thats history. Pax Americana has effectively come to an end with the Taliban giveaway. The official end will be if/when they abandon Taiwan; and thats why people care so much. If US can't intervene to save its allies then their word means shit. US has become complacent, self-absorbed in its own problems and as every "empire" crumbling from within. The signs are pretty visible both economically and socially and I won't expand because it would take a whole essay. Point is, when an empire stumbles, others run to take its place (or a piece of it). Of course, there is the asterisk of nuclear weapons that ensure MAD but I bet that millions or billions of man hours are spent on finding ways to avoid MAD on both sides. If that will result in MAD in the end , I don't know; but I don't think its a deterrent which is as real as it was in the 60s.
How close are we? I would put a timeframe of 10-15 years if no other major event comes up. Because US is not what it used to be 10years ago even. The fuckup in north africa was the start, the absolute plunder in Afghanistan was next. People in US are tired of wars as inequality grows and the political system offers no exit. Couple this with a societal swift towards postmodernity thanks to the arrogance of the "elites" and you have a great mix of angered populace with no regards to rationality. Now the war in UKR creates a fundamentally unstable system in the heart of Europe. This system will have to stabilize one way or the other, Russia cannot remain a pariah for a long time or it will risk making it even more aggresive. China is asking for "lebenraum" in southeast sea which US doesn't want to give (but IMO they will be forced to). If China decides to take Taiwan the option is either war with china in their backyard, or backing out and accelerate the US downfall. Either way, it won't go out without a boom, it never does.
Newer generations in advanced countries (including me) view war as something extraterrestrial but reality is that its an everyday phenomenon for the biggest part of the world and for the most time in history. So its easy to think/hope that it will be like this forever and "war is finished", but Ukraine showed to most Europeans that its not (and IMO thats what shocked them the most)