I guess it depends on the basic living standard. If you say, I can not work and keep the same standard of living I have now then I'd probably travel more.
Take a motorcycle trip around the world or something like that. Canoe down the nile. Sail to Antarctica. Stuff like that.
I would still program computers, probably around AI and cyber security, network security. Sleep lots because I love it. Spend a few hours a week doing something new.
Sounds amazing, where do I sign up?
Volunteering, gardening, fixing up old cars. I'm sure I would pick up some old former hobbies and/or some new ones; for instance I'd like to learn to play drums. I don't think I would do much with computers, at least in the way of programming. I've done plenty of that and there is a lot more to life. With volunteering as well, I wouldn't want any of it to be computer-related.
I have been thinking about this quite a bit because I hope to exit the workforce soon. I'm very tired of working in tech, and corporate America generally.
Tangential, I've wondered recently if it's possible to work only when you want. A lot of people talk about working just enough to pay for necessities, but I'd rather work a little bit to cover those necessities, then have most of my time where I can either live or choose to work on demand, i.e. to support hobbies that can get expensive.