Here in the US we go the opposite way: even if you do find some way to take enough time off to accomplish something significant, there's a good chance your employer (legally) owns it.
No worries for Amazon SDEs! The amazon software developer "outside contributions" agreement basically states that you are not allowed to do anything without approval anyways. /s
Seriously tho. When I was employed by them their agreements were by far most draconian compared to any other company I've worked for. Ridiculous.
Most companies I've worked did have a route to enable you to contribute to projects outside of work and still retain the rights. Tho the easiest route is to establish something within a domain you want to work and then state that on a "inventions and copyrights" pre-employment agreement. This will outright eliminate you from certain jobs but... That's the US for ya.
And when you go without a job to try your hand at starting a business, it's usually accompanied with the gamble that you won't need any medical service that will wipe our your savings.
b) Define "something". If I take a year off to e.g. write a novel, do you really think that gap in my resume isn't going to affect me negatively if/when I start looking for jobs again?
Here in the US we go the opposite way: even if you do find some way to take enough time off to accomplish something significant, there's a good chance your employer (legally) owns it.