Imo upper class should be limited to the ability to live the rest of your life without working ever again. Otherwise there’s no meaningful distinction between middle and upper class. Stuff is stuff, and more expensive stuff but no other significant separators isn’t enough to put regular Harvard alum in upper class. If they permanently lost the ability to work, they’d die too.

Class should always be about means to live— middle class should be able to comfortably live and be able to survive bouts of unemployment. This is sadly not the case anymore (though I argue it is because the middle class is simply disappearing), but by letting the meaning erode, we allow the uppermost classes to acclimate society to lower standards. The middle class should be able to go some weeks without employment. The middle class should be equally comfortable as standard non-founder Ivy alum, cheaper stuff notwithstanding. There can be differences of luxuries and ability to move up, but anyone working full time should be comfortable, housed, and not fearful of a layoff or hospitalization.

Then upper class should be those who could quit forever and continue to live. Ofc, in an ideal society, everyone should have means to live, not merely the middle and up. In America this is not the case though.