Why would I use the proxy instead of direct call to RealSubject?

I’m actually reading about the Proxy design pattern (https://refactoring.guru/design-patterns/proxy) and I’m wondering about what does prevent the Client to call directly the RealSubject class.

I give you this illustration that i’ve found on this post :

I can’t understand how to prevent client for making the mistake of calling the RealSubject directly instead of the Proxy object.

What I would like to do is to obligate the client to call the Proxy object, so the Proxy object can filtering access and logging access ect…

I’ve even buy this book and read the part about Proxy, and have also looked at the code example which is given :

...
Proxy design pattern code
...
echo "Client: Executing the client code with a real subject:n";
$realSubject = new RealSubject();
clientCode($realSubject);

echo "n";

echo "Client: Executing the same client code with a proxy:n";
$proxy = new Proxy($realSubject);
clientCode($proxy);

So here in this code snippet it seams to be allowed to call directly the realSubject without using the Proxy.

So maybe I’m not looking at the good design pattern, maybe there exist one which would suit my requirement of forcing client to call the ‘Proxy’, and not allow to call the RealSubject ?