Gluca23 You should understand that
the storage scopes feature allows apps to create files as they typically would and allows them to access those files, just like how it would work on stock Android. Where storage scopes is different is that it allows whitelisting which specific directories and files the app can see.
Using storage scopes with WhatsApp would allow it to see the data it's created for itself, but you can then chose exactly what other data like your pictures or downloads it can see. So no way to break WhatsApp using it.
Further reading can be done here.