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):

const { items } = event.detail;
            while (selectElement.length !== 0) {
              selectElement.remove(0);
            }
            for (const item of items) {
              const { displayValue, exportValue } = item;
              const optionElement = document.createElement("option");
              optionElement.textContent = displayValue;
              optionElement.value = exportValue;
              selectElement.append(optionElement);
            }
            if (selectElement.options.length > 0) {
              selectElement.options[0].selected = true;
            }
            storage.setValue(id, {
              value: getValue( true),
              items: getItems(event),
            });
            selectedValues = getValue( false);
          },
          indices(event) {