Reading from the source code:

https://github.com/mozilla/pdf.js/blob/57d196e3497e77c81c19f852715ce79d9fb91492/src/display/annotation_layer.js#L2846

it appears to me it was not an intention to mark downloadManager as a required parameter in AnnotationLayerParameters:

https://github.com/mozilla/pdf.js/blob/57d196e3497e77c81c19f852715ce79d9fb91492/src/display/annotation_layer.js#L63

and AnnotationLayerBuilderOptions:

https://github.com/mozilla/pdf.js/blob/57d196e3497e77c81c19f852715ce79d9fb91492/web/annotation_layer_builder.js#L40

and it should be optional, similarly to accessibilityManager for example:

https://github.com/mozilla/pdf.js/blob/57d196e3497e77c81c19f852715ce79d9fb91492/web/text_layer_builder.js#L30

**Configuration:**
- PDF.js version: 2.11.174
- Is a browser extension: no

**What is the expected behavior? (add screenshot)**

`downloadManager` to be optional

**What went wrong? (add screenshot)**

`downloadManager` marked as required

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

enableScripting: this.enableScripting,
      hasJSActions,
      fieldObjects,
    });
    
    
    if (this.linkService.isInPresentationMode) {
      this.#updatePresentationModeState(PresentationModeState.FULLSCREEN);
    }
    if (!this.#onPresentationModeChanged) {
      this.#onPresentationModeChanged = evt => {
        this.#updatePresentationModeState(evt.state);
      };
      this._eventBus?._on(
        "presentationmodechanged",
        this.#onPresentationModeChanged
      );
    }
  }
  cancel() {
    this._cancelled = true;
    if (this.#onPresentationModeChanged) {
      this._eventBus?._off(
        "presentationmodechanged",
        this.#onPresentationModeChanged
      );
      this.#onPresentationModeChanged = null;
    }
  }
  hide() {