Parental leave is paid. If they can't survive 6 months unpaid leave from a worker, then they got a problem. The system with paid leave works fine in all of Scandinavia so how could unpaid leave not.
In Canada I get leave but I get paid by the Employment Insurance program (tax). Interestingly it caps off meaning lower income people might get 100% of their salary while I'd get like 30%.
What would that minimum window look like to my hypothetical employer if I decided on a whim to start a business tomorrow?
similarly, you can't just take this business leave by saying "I'm not coming in next week!". The notice period is actually longer than for parental leave.
That's on par with parental leave, where it's not uncommon to tell the employer 3 months before the delivery.