How about anything that tracks the user's behavior and changes its output based on that behavior specific to that user. If I have a table somewhere in my software that identifies a user and references behavior, not intentional settings, just behavior and that is used to determine what the software does. Make that illegal and a lot of problems go away. To me it is this feedback loop that is insidious.

It's fairly obvious what "short form content" is in context of discussions around TikTok, Reels, Shorts etc.

Let me add, it sound very much like 3D-prohibition for guns. The total demonization of anything, because it could be bad, given certain conditions, is a recipe for disaster. As you say, is extremely difficult to define where are the limits, and the extremely hard to apply the limits without screwing over millions.

study each proposed form of short form content regarding impact on cognitive function and select the most destructive forms for legislation.

if you make a website that provides short form content you are subject. why would an aggregator be excluded?

go ahead and let users make multiple accounts. the current, invalid, answer here is biometric provisioning (done not to protect anything but government and corporate interests). personally I don't care if an adult wants to fry their brain, provided that they have been adequately educated as to the extent of what they are doing to themselves. it's why I included the parental proviso, because protection from brain frying is most important during childhood.