It's most certainly not a blanket "Everybody who is not in compliance with the GDPR will get a 20 million Euro fine".
Secondly and most importantly, GDPR is not about preventing people to get information, but rather about preventing people to track customer. If I use your example, GDPR would prevent you from following someone after they watched you juggling. It would prevent you from following them home, noting where they work, who are their acquaintances, what kind of food they eat and so on: it's technically legal but incredibly creepy. If someone were doing this to you you would be the one to tell them to piss off. You can perfectly write what are the observations of the passer-bys who watched you, as long as the log is anonymized. Which is easy to do and not harming for your business. You didn't want to track them anyway, did you?
No, you'll just sell it to the highest bidder. And enough people do this in such an underhanded way that the EU decides to regulate the shit out of you. So maybe you should have asked permission before recording identifiable people's behavior or otherwise earned their trust. Instead of being shady and myopic about it.
Anyway, it is not the act of having the information about other people that is problematic, it is the act of collecting, using, or sharing it. Do you think I should be able to follow you around and write down every step you make? Should I be able to use that information in every way I want? Do you want me to tell your significant other what you actually did on that »business« trip, tell your coworkers what you got from the sex shop? Should your doctor be able to tell everyone about your health status, your bank about your financial status?
It is just naive to pretend that handling information is inherently without any concerns and therefore no rules should apply at all. And it is just silly to pretend that writing down an observation you made in the park in a notebook is the same and should be treated in the same way as systematically collecting information about every website visitor.
And your examples are not all the same. If you’re in public, you have no reasonable expectation of privacy. So yeah, take all the notes about me you want. That’s entirely different from my doctor sharing my health info.
And while you personally may not have any expectations of privacy in the public, that is certainly not true in general for everyone and in every country. Here in Germany the constitutional court ruled just this week that having a dash cam in a car violates the privacy rights of the people you capture.
You are also generally not allowed to take photos of people in the public without their consent. It is not a problem if they randomly appear in a picture you took of a building or whatever, but you are not allowed to take photos were people are the main motive.
To put it another way, I go to Central Park and start to juggle. I don't charge people, I just juggle because I like to juggle. Some people watch; others simply ignore me. I write observations about a couple of the people who watched me perform in my journal. One of those guys was from France. He later looks me up in a phone book and calls me to demand I give him any observations I wrote in my journal. I tell this fellow to piss off. A few months later I get a letter saying I need to pay 20 million euros because I wouldn't give away my personal observations stemming from something I did publicly and for free.