I'd suggest that kids who are younger (say up to around 13), increasingly have unrestricted access to the internet/tiktok etc., but they are much less likely to have enough control over devices to download apps. While that doesn't cut off all routes, it's still a barrier for many.
The overall act is clearly far from foolproof, but it's still a fence between kids and content we know they shouldn't be seeing. Some kids will climb the fence, others will see it and decide not to. What won't happen, which does now, is the kids who don't want to be on the other side of the fence (e.g. with self-harm content), end up being led there by an uncaring algorithm.
The interview this morning from Peter Kyle was pretty controversial, but one thing he did say was that it's not expected to stop 100% of kids- but even if it stops 60% that's a huge win.