await browser.actions().mouseMove(Element).doubleClick().perform();
await browser.actions().doubleClick(Element.getWebElement()).perform();
the above 2 codes works properly to double click on any element when it's visible on screen.
Here Element is
"let Element = element(by.xpath("locator"));"
Below code did not works as a msg is shown saying
"Failed: JavaScript error: arguments[0].dblclick is not a function"
whereas when checked in console similar scripts did worked to double click the item: "$($x(element(by.xpath("locator")))).dblclick()".
Will update my comment if able to find the exact JavaScript syntax to make below code run.
await browser.executeScript("arguments[0].dblclick();",
Element.getWebElement());