We could use:
https://github.com/mozilla/pdf.js/blob/c3d08580627471432a6ad0b2fdb948df64126afa/src/display/api.js#L929

and look at bit 4.

The following pdf:
https://orimi.com/pdf-test.pdf
is not editable in neither Acrobat nor Edge nor Foxit and nor Okular.
pageDiv,
    pdfPage,
    l10n,
    annotationStorage = null
  ) {
    return new AnnotationEditorLayerBuilder({
      uiManager: this.#annotationEditorUIManager,
      pageDiv,
      pdfPage,
      annotationStorage:
        annotationStorage || this.pdfDocument?.annotationStorage,
      l10n,
    });
  }
  /**
   * @param {HTMLDivElement} pageDiv
   * @param {PDFPageProxy} pdfPage
   * @param {AnnotationStorage} [annotationStorage] - Storage for annotation
   *   data in forms.
   * @returns {XfaLayerBuilder}
   */
  createXfaLayerBuilder(pageDiv, pdfPage, annotationStorage = null) {