I am unable to click elements of shadow dom elements.

var propelement = await wdriver.findElement(By.xpath('//*[@id="rptLoadingFrame"]'));
var pdf_url = await propelement.getAttribute('src')
wdriver.get(pdf_url);
//var download1  = await wdriver.findElement(By.xpath('//*[@id="download"]'));
//download1.click();

await wdriver.executeScript("document.querySelector('#viewer').shadowRoot.querySelector('#toolbar').shadowRoot.querySelector('#downloads').shadowRoot.querySelector('#download').shadowRoot.querySelector('#icon').click()");

Getting below error message

JavascriptError: javascript error: Cannot read properties of null (reading 'shadowRoot')

1. PDF viewer is embedded within iframe and no DOM visible accept <slot> element inside Embed element with #Shadow Root (user-agent)

   

2. When I access SRC mentioned in iframe got below DOM i.e. PDF viewer. I want to click "Download" button to download the PDF.