I live in Belgium, didn't inherit millions from family and am in the middle working class. I'll stay in this working class, this is how it has been conceived, I'll never make millions. Once I understood and accepted this, I managed to work only 4 days a week and live more than finely with this salary. Work is only there to get my living wage, I detached completely from work life, I chat with colleague, I do what I'm supposed to do, nothing less, nothing more, I play cards and read a lot, then my 7h50 workday is over and I go on with my real life: my son, my car, my hobbies, my friends. THIS is what counts.
At the same time, I am looking for a part-time freelance job out of Belgium, and find it surprisingly difficult to find.
I am omnivore, having successfully maintained both outdated Eclipse/OSGI-based codebases and large PHP websites, but everyone wants to buy me in entirety.
I think it might be because if you just want part-time it may looks like you are not going to take it seriously.
Being freelancer is more difficult for the not long term, but the best to achieve shorter working hours I would say is, work full time for 9-12 months, then you know how things work and also have some "power" to request part-time.
The problem of course is that after 2-3 years you will most likely change job again, so it does not last too long as long as you want higher salary
There are many self-made millionaires. Not sure if you are a dev or not...but you can always make an app or a game that takes off? Your life circumstances may lead you to the app and you could make it out of necessity for yourself.
Honestly, I'm content with being in middle class but I also think about future opportunities and work towards bigger goals.