That part has (maybe-ish?) changed with these most recent amendments. Per the EFF:
The Bill’s Knowledge Standard Has Changed
The first change to the bill is that the knowledge standard has been tightened, so that websites and apps can only be held liable if they actually know there’s a young person using their service. The previous version of the bill regulated any online platform that was used by minors, or was “reasonably likely to be used” by a minor.
The previous version applied to a huge swath of the internet, since the view of what sites are “reasonably likely to be used” by a minor would be up to attorney generals. Other than sites that took big steps, like requiring age verification, almost any site could be “reasonably likely” to be used by a minor.
So in a best-case interpretation under the new text, a site whose ToS does not allow minors to use it would not be required to check everyone's ages to verify no one is a minor, in order not to be liable if a minor accessed adult content on it. The problem is, the bill isn't actually explicit about what qualifies as the site having knowledge of children using it means:
Requiring actual knowledge of minors is an improvement, but the protective effect is small. A site that was told, for instance, that a certain proportion of its users were minors—even if those minors were lying to get access—could be sued by the state. The site might be held liable even if there was one minor user they knew about, perhaps one they’d repeatedly kicked off.
The bill still effectively regulates the entire internet that isn’t age-gated. KOSA is fundamentally a censorship bill, so we’re concerned about its effects on any website or service—whether they’re meant to serve solely adults, solely kids, or both.
No site is going to want to be the ones that an AG tests out their new lawsuit hammer on, so it's likely to end in 1 of 2 ways: either verifying the ages of all users of the platform, or prohibiting all user-generated content to prevent adult content being posted. Republicans are fine with either of those outcomes. The sad thing is the Democrats who either also are, or who don't understand the impacts but are voting on it anyways.