It's my understanding that all federal lands such as parks and national forests as examples, flying is prohibited without prior written authorization... It's the local city and state rules that become a little less clear since they can vary from location to location.
The other issue I see commonly is the question of when does a flight become a commercial one that requires you pass tests in order to be licensed for that. The example would be like those of Youtuber's and other streamers that also include flights in their video's yet really don't get enough compensation by the ads on their video's to be called an actual wage. I'd still classify many of these as hobbyists or non professional video artists and not a fully commercial entity. At what point does a hobby become a commercial entity.
Tony has already mentioned several times that the weight limits of what is a toy and what is a hobby aircraft are unreasonable. There are certainly toys out there that exceed the weight limits and it seems, typical of a bureaucracy agency, that these weren't very well thought out. In other words, once again people that have no clue on what they are making rules for... make them despite their ignorance of the subject they are ruling on.
The FAA is a large agency created to address large commercial and private aircraft. They have a lot of experience in those areas but little in the area of the hobby itself. While I'm sure there are many FAA employees that do also fly RC aircraft, those aren't the ones that decided on what rules were needed or required. They should have created a section just for the RC hobby and put in people that actually have experience before deciding on any rules they needed to implement.