Will people find new work to do? And if they do, why wouldn’t AI follow them into their new industry and undercut them there, too? So perhaps it’s not “people will find new uses for their money”, as people won’t have any money to find a use for. Perhaps instead, businesses will find new users of money - the AIs who are now doing all the jobs. At least in principle, I don’t see why there couldn’t be an economy that’s just businesses and agents.

Let's not ignore the economy where the agent is the buyer.

Video editing and website design being the example here. If the video is an ad, or the website is a sales site, if an agent is a buyer these change considerably. That is an entirely new economy, similar to how we did not understand the knowledge economy until it was fairly well developed in the mid 1900s (someone smarter than me might have better info here).

I have no doubt the economy will change, but we as humans operating in the world will still have needs that need to be met.

In addition, with a shrinking population in all developed nations, we may well still have a shortage of workers in 30 years, not an oversupply.

The science fiction theory is that in the end, work is mostly done by AI/Machines and so people can have access to food, products, whatever they need for almost free or at least there is no need to work anymore and everyone can enjoy a beautiful life.

But in reality, a few trillionaire like Musk will capture most of the value/income that they can from the society advancement dividends and a bigger and bigger percentage of the population will become poor, exploited, and depending on the charity of the happy few.

This explains why large scale unemployment is not preferable even for capitalists. But this is well known and the policies are usually made to prevent it.