* Negotiate shorter workweek at your current job. Many people have successfully done this to reduce workweek.
* Become a consultant or contractor. If you do it right (and that's hard!) you can work shorter workweek. Or you can do OK and work shorter workweek and make less money.
* Negotiate shorter workweek at new job. This is much harder, but doable.
In my case, I was a consultant, got part time job with one of my consulting clients, then negotiated short workweek at new job. First two (consulting, first job) were <30 hours a week (when I started, at least), second job was 35 hour workweek.
(Also, every once in a while I've seen part time jobs advertised.)
Talk a bit more about this here (https://codewithoutrules.com/saneworkweek/), and a lot more in book which will be available as soon as I write the sales page (sign up at that page to hear about it).
(source: https://www.youtube.com/watch?v=3zc4bGkU05o)
This was also popular in Slashdot comments.
Expect 1 year of underemployment where you have either no work, or strategically discounted/pro-bono work so when you are doing something it's 60 hour weeks for shit pay.
Once you have a couple clients in your portfolio you can spend another year or two making normal consultant wages, but as you will be focusing on becoming know you can't turn down any work so expect 40-60 hour weeks.
Finally, after 3 years you'll have a solid reputation and if you played your cards right, work should start to find you. You can put less effort into marketing and start managing shorter weeks.
Don't go this way if you want something easy though. It's nothing of the sort. But I can smell the freedom and I see the light at the end of the tunnel.
But I guess the easiest way is becoming a freelancer. Just tell your clients you only have 20h a week time.
You also have to ask the question, what is work?
I mean, if you got a dev job, you aren't coding 40h a week. Yes, on a good day it's 8h, but you probably won't have 5 good days in a row. So, how much do you really code in your 40h, how often are you doing something else? Also, how often are you thinking about job related problems while not getting paid?
I don't follow, what's the goal here?
People regularly deliver a value that nets them a good income without putting in 40+ hours a week.
On a related note, it's also really hard to distance yourself from people who "are doing it wrong" in general. I can't tell you the amount of effort I've had to waste learning a topic that from a distance I could vaguely tell was not worth learning, just so I could have reasonable arguments as to why it's inferior to some other idea. This is particularly frustrating in tech because of the complexity of many tech stacks, that just getting to a point where you can sound like an expert just to provide counterpoints can be exhausting.