"Only the app.component is Serverside rendered. All other components are still then client rendered". How do you know that all the other components are client rendered ?

Open the source code of the page you want to test using Google Chrome. Not "inspect", but show "source code". If the <app-root></app-root> is empty, then the current page is generated at client side. But if the <app-root></app-root> contains other elements, the current page is generated at server side, so you don't need to do anything else.

I know it can be confusing if you expect the whole page to load and your browser's loader to spin like it does with PHP, but it works differently with Angular.