For what it's worth, turk73's attitude regarding work only being a means to earn money is just as misguided and narrow-minded.
Sitting on a beach forever is okay, if you like that sort of thing. It's also okay to write a novel that no one will ever read, or to crash remote controlled helicopters and then repair them. It's also okay to plant a hummingbird, butterfly, and honeybee garden, and buy a big macro lens. Or maybe ride a motorcycle all over the continent. Or move to Florida and do Florida things. Or move to Wyoming and manage a herd of 15 cattle on a plot that the real ranchers call "Flyspeck Ranch". Or open an ice cream shop that turns a profit only 20 days per year.
Retirement is as varied as the people who are no longer bound to conform to a work standard.
Try this thought exercise: if you suddenly became a billionaire, and didn't need to work for a paycheck any more, would you continue to write software (I'm assuming you're a developer like most on here)? Personally, I would. I probably wouldn't do it 8 hours a day, but I'd find some fun project to work on, and spend some time on that. It'd be my hobby, when I'm not doing something else I enjoy like traveling or skiing or whatever. I didn't get into this field just for the money, I did it because I like computers.
Buffet likes investing. What else is he going to do with his spare time?
But the job market doesn't seem to support that, so it's full time or no work for me (unless I put in the huge effort to build up a freelancing portfolio, which doesn't seem to be as much of a job market in ML yet?). Given the choice, I'd choose no work, and make my own work for fun.
Personally, I could easily work on some kind of OSS project if I suddenly found myself with lots of free time. I can do C, C++, Python, etc., so it wouldn't be hard for me to find an existing project to contribute to, or make my own.
And depending what you're doing, it can require ridiculous computational resources (like hundreds of thousands of dollars to train a model), but that's far from the norm. If you aren't trying to advance a couple particular states of the art, you can get by with a fancy computer and patience, or a pretty reasonable AWS/GCP bill, probably comparable to any other fairly expensive hobby.
I agree about the part-time thing too; considering how much of a skills shortage the industry is constantly crying about, and how well-paid developers are (which means that, if they live frugally and don't have kids, they don't really need to work to retirement age if they don't want to), it really should be possible to have part-time positions for people who want to stay current and work on interesting problems but not have to dedicate themselves to it full-time, and not be stuck only doing OSS stuff (which is great, of course, but not really doable with some fields).
And people will also necessarily have different preferences on how to spend their time and energy, and different amounts of time and energy as well.
Would also like to point out that "sitting on a beach forever" is not the negation of spending all your time an energy on solving the problems that the capitalist economy rewards.
There's plenty of people out there who have a passion for things that aren't expected to earn money, but for whom the best option for actually making money is something that's quite boring.