This is the most common way for people to get part-time work. Don't even need legal right to do so, though it helps, e.g. I know people who have done this in US

This is the most common way for people to get part-time work. Don't even need legal right to do so, though it helps, e.g. I know people who have done this in US where your rights as an employee are... not as good. Here's why: you've been at company for a while. You know the code, you know the dependencies, you know the business logic, you know who to talk to, you know the mindset, you know the priorities. Replacing you is expensive. Even if they can hire someone with same skills on paper, there's a long and costly organization-specific ramp-up for most companies. Thus, a good rational manager (not all of them are, obviously) will prefer to have you part-time than to have you leave. Which gives you negotiating leverage. The longer you've been at a job, the more valuable you are, the better this goes. Even better if it's a tight hiring market, like now. (I write about this at length in my book, Programmer's Guide to a Sane Workweek: https://codewithoutrules.com/saneworkweek/. https://codewithoutrules.com/saneworkweek/.)