Or you just buy stuff which is mostly zero sum, such as more real estate or more services which simply have no productivity gains to be found as they are based on time/the human being human.

You see that here in Canada and in the USA. The amount of dwelling space we occupy has soared even as families shrink. My Dad grew up with a family of 5 in 1200 sqft. Canadians today consider that a shoebox that barely fits 2.

I would bet that income gains are disproportionately directed to buying more house or additional houses, no matter the income.

Or you buy more massages or more tutoring or more other various services that simply cannot be multiplied 100x as the human is an integral part of the service rather than a stand in until the robot is ready. How does a massage therapist massage 100 people at once?

But that's not what we are talking about here. We are talking largely about innovation, the productivity boom was the period people went from horses to cars. Selling shiny new things to replace the same things with a patina and calling it productivity is like breaking windows to fix them and calling that productivity. So you expect to see a plateau in truly productive car manufacture for example (that manufacturers hope to squeeze revenue beyond with unproductive manufacture, such as planned obsolescence, things that can't be sold on the secondary market, etc) but you don't expect to see an overall plateau of productivity unless 1) innovation is stifled or 2) everything that people could possibly need or want has been invented. I don't think the latter is true.

Tell this to the advertising algorithms that want to always advertise whatever I've most recently purchased.

Once you have one ergo keyboard you don't buy a hundred ergo keyboards.

looks at desk

......fuck

Humans are deeply weird...