createComponent-5.ts

  openDialog<T>(dialogContent: Type<T>) {
    const footer = document.createElement('p');
    footer.innerText = 'footer';
    
    const dialogContentRef = createComponent(dialogContent, { 
      environmentInjector: this.injector 
    })

    const dialogRef = createComponent(DialogComponent, {
      environmentInjector: this.injector,
      hostElement: document.getElementById('dialog-container')!,
      projectableNodes: [
        // ng-content nodes
        [dialogContentRef.location.nativeElement],
        // second ng-content (e.g <ng-content select="footer"></ng-content>)
        [ footer ]
      ]
    })

    this.appRef.attachView(dialogRef.hostView)
 }

Good, but if you have dependencies in your dialogContent, it won't be 'loaded'. For exemple, if you have a Angular Material input, it won't work. It works only in you have simple HTML.

Aaaah, found the solution :
You have to attach also the view of the first component you have created to the CD cycle:
this.appRef.attachView(dialogContentRef.hostView).
If you don't do this, the dependancies of the first component won't be correctly working.