Why can't I block most of the apps (iOS)

When you block apps individually you disable Internet access for the app.

Unfortunately, not all apps can be blocked like this.

The full list of blockable apps you can find here.

If you want to block all the apps individually in Child mode, you need to have a desktop device to connect your child's device to it and set up our Advanced Features.

You can find the installation process on the following page:

How to set up the Advanced Features