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.
return new XfaLayerBuilder({
      pageDiv,
      pdfPage,
      annotationStorage:
        annotationStorage || this.pdfDocument?.annotationStorage,
      linkService: this.linkService,
    });
  }
  /**
   * @param {PDFPageProxy} pdfPage
   * @returns {StructTreeLayerBuilder}
   */
  createStructTreeLayerBuilder(pdfPage) {