So it’s OK for Russia to invade Ukraine then since NATO expanding is a problem in their opinion that needs to be “nipped”.
Its not always a question if it's OK.
The unsaid rule here that people have forgotten, ironically due to the post-ww2 US led world order, is that what is OK and acceptable is determined by who sets the ground rules and controls the global order. All this talk of war crimes, international law, etc is often levied as criticism towards the west when ironically, it is the west who setup these political mechanisms in the first place so the entire world doesn't descend into a might makes right and dog eat dog shyt fest that led to the previous world wars. Ukraine fate will not be decided by what is right or wrong but whether the west supports them long enough to grind Russia down to at least a stalemate or the west decides to sacrifice Ukraine due to lack of political will at home to continue to support them. Right or wrong doesn't matter.
If Russia for example wants to attack a NATO country due to some perceivedprovocation of NATO expansion threatening their interest, then they are free to. It's not a matter of if it's OK but if they should and could. Most people would agree Russia would be dumb to do so.
In this case, if you're a government of the US and your goal is to minimize an escalation of attacks on the US, it's all up to personal interpretation. Some say maybe the US should become isolationist and remove all troops from overseas and that will fix the issue. Others believe that allowing a relatively small case go unanswered will lead to bigger problems down the road. Personally, I believe in the latter but there is no right or wrong answer imo.