NAL, but looks like they're alleging something like negligence & deception. Addictiveness is just the mechanism of harm, so doesn't require a strict general case: just actual harm and the prior knowledge thereof.

So like the general argument is "company X was causing material harm, knew they were causing harm, and actively decided to continue causing harm while covering it up."

It'd be similar to suing someone who sold a dangerous toy under the label "safe for all ages". The lawyers don't need to ban specific features (sharp edges, fast motors, etc.). They just have to argue the way it's put together harms kids, the company knew about it, and they kept lying about it anyway.

The remediations could therefore be case-specific. They don't need to ban infinite scroll in general, just ban Meta from applying it to their products, since it's known to be harmful in that context.