The differecne between ww2 and these wars is that in ww2 we actually fought a war, in vietnam and afghanistan we played at war
this is true. additionally, even if the US had done total war in Afghanistan, running the country would be nearly impossible given the lack of functional (by 1st world standards) government institutions and just generally shitty infrastructure
however, this
Even russia isn't fighting a war, if so they could just nuke or bombard ukraine afterall.
isn't entirely true. Russia wants to exist long enough to possess more of Ukraine, so their nukes are not an option. but, in addition to that, their strategic bomber fleet is irreplaceable at the moment. they have to stay far out of Ukraine and solely use cruise missiles, because if they get any closer they'll be shot down
russia's main problem is that they're fighting a 21st century war using late 20th century tech and mid-20th century strategic / tactical mindsets. Ukraine doesn't have the numbers that Russia has, but they've got the brains and the tech.