The law would define a social media platform. Maybe something like: The term “social media platform” means a website or internet medium that— (A) permits a person to become a registered user, establish an account, or create a profile for the purpose of allowing users to create, share, and view user-generated content through such an account or profile; (B) enables 1 or more users to generate content that can be viewed by other users of the medium; and (C) primarily serves as a medium for users to interact with content generated by other users of the medium. [https://www.law.cornell.edu/definitions/uscode.php?def_id=42...]

If your SaaS app met that definition of a social media platform it would be illegal for you to show content in an infinite scroll window. Because your application targeted business users who paid for the service, people would be less likely to sue you. Maybe it'd be worth it to you to include infinite scroll anyway. Companies knowingly break the law all the time after calculating that even on the off chance they get caught the fines they'd face will probably be less than the profit they'd make. The larger your platform got, the less worth it breaking the law could become and of course if the public felt the fines were so low as to be ineffective, the law could be amended to increase the fines.

The law could even allow some platforms to include harmful content like infinite scrolling if certain conditions are met. For example, platforms could be allowed to include infinite scrolling if they require a credit card to sign up, and they display a warning explaining that the platform uses infinite scrolling which has been determined to be harmful by promoting addictive and compulsive behaviors, and it provides an option to disable that feature. Still, it's probably better to widely ban those kinds of practices that serve no purpose other than driving engagement/addictive behavior. We can just decide as a society that we value people's mental health more than maximizing tech billionaire profits.