It is only anecdotal evidence of course but I went for 24 hours a week back in 2019 and my employer (a ~unicorn scale-up in the Amsterdam region) was not fussed

It is only anecdotal evidence of course but I went for 24 hours a week back in 2019 and my employer (a ~unicorn scale-up in the Amsterdam region) was not fussed about it at all. I'm a software dev and was one of the two employees with in-depth knowledge about a crucial part of the stack, so I had more leverage than most, but still the response was so much "yeah of course, we have to allow this by law" that I would be surprised if any of my colleagues would have had a different response.