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.
if (
      this._spreadMode !== SpreadMode.NONE &&
      this._scrollMode !== ScrollMode.HORIZONTAL
    ) {
      return 2;
    }
    return 1;
  }
  _setScale(value, noScroll = false) {