Then don't pin to a dollar amount, pin to relative wealth available in the world/country/region. Something like estimated total accumulated wealth / total pop.

Inflation destroys the value of money, not the underlying goods or services. Whether there are 100 dollars to go around or 10 billion, for the same "physical context"/material reality a rule along the lines of "no more than %5 of total wealth accumulated in 1 person's account" seems inflation-resistant.

So a wealth cap would also help to fix the insane inflation of house prices? Is there a downside?

This is a common response but who's problem are you solving? How many people are affected by this? And it seems modern state banks aren't as scared as inflation at the macro level, why do we need to be concerned?

How about this — we all agree that the entirety of wealth in the universe is made up of 21 Million bitcoin. Then the wealth cap is 21 million bitcoin. Of course, nobody can have it all, in fact, if they try they will only drive up the relative cost per unit.

If this seems insane to you, consider the insanity of trying to define a fixed container size with an infinite flow of water.