Fixed wealth has become a very difficult concept to define with the advent of electronic debt booked as assets.
To me, "fixed wealth" implies something you possess which cannot be simultaneously possessed by another (I have this double eagle, therefore you don't have it) AND which cannot be taken from you other than by force.
Not sure how much fixed wealth there is, but it's a lot less than most people seem to believe.
Wealth could also be attributed to sweat equity, would it not? That of course is based on productivity, so it’s obviously fluctuating, but one could easily factor that into their asset category, something that can be generated and traded for goods.
Obviously banks don’t consider this but it’s quite important. Just ask China.