As an independent professional, you have the freedom to work anywhere you want. This can of course be done at home in the study, but that can still be lonely. There are several flex work places in the Netherlands where you can do your work among people. At many locations you pay a certain amount to be allowed to work there, but there are also many places where you can work (almost) for free. Some examples.
At Seat2Meet you can book a flex workspace for free. At least, you don't have to pay for it with money. You pay with social capital, which means you have to be willing to share your knowledge and skills with anyone who can use your help. You must reserve your workspace online in advance. If all the free spots are taken, there are also paid spots available. You pay a few euros per day for these. Seats2Meet can be found in Amsterdam, Groningen, Utrecht and Hengelo, among other locations.
The coffee chain Coffeecompany is spread throughout the country. And no matter which establishment you visit, there are always people sitting with laptops working. They are busy places though, so if you really need to concentrate it might not be the best place. But cozy it is. There is free Wi-Fi in every Coffeecompany. This is only available to paying customers, though. As long as you order drinks you can go here.
What applies to Coffeecompany also applies to Starbucks. Free WiFi is available for paying customers. You can get your work done with a cup of coffee at the table or plop down in one of the large armchairs. Since it is a catering establishment, it is not quiet work here either. A great place to do chores that require a little less concentration.
These examples are just a few places you can go as a self-employed person. If you search in your neighborhood, you will find many more. Almost every catering establishment offers WiFi these days, so probably that one lunch spot near you will too. Many hotel bars also allow flex workers. As long as you are a paying customer, many catering establishments welcome you with your laptop. However, there are also restaurants and cafes that prefer not to have laptops in their establishment. Therefore, always check this before opening your laptop.