Tax withholding’s vary from country to country and holding back a percentage is not uncommon.
A good primer
https://partner.steamgames/documentation/payment_info
If you release through Steam and don’t do the paper work then you would be on the hook for 5% to Epic whatever cut Steam tasks plus a 30% tax withhold.
If you are planing to set yourself up as a freelancer a good place to start is your own bank as they can provide you with the basics and the services by setting up a business account but i your game goes Angry Birds then the first people you should be hiring are lawyers and accountants.