It was about five minutes of filling a form with the national authority.

There are some responsibilities that you get along with it (e.g. you're supposed to do risk assessment and document your approach to risks and security, etc.) but you don't actually have to deliver those documents unless they ask for it. They may also require you to respond to some questionnaires and such (I've received only one questionnaire over the years; they were conducting a study about how registrars verify the identity of their customers). Obviously these are primarily intended for commercial operators who have responsibility for customers' domains, and my risk assessment offering domains for myself is going to look pretty simple so I haven't actually written anything down. Will do if/when requested.

Excerpt from my whois records:

    Holder
    
    holder.............: Private person
    
    Registrar
    
    registrar..........: Private person

(It used to have my name along with other info in the registrar field, but this thankfully changed following GDPR)