If double clicking on an attachment is not working in Microsoft Outlook 2016, Outlook 2019 or Outlook Microsoft 365, a solution could be just to change the double-click speed in Mouse Settings.
Follow these steps:
Click on Start
and type Mouse in to the Type here to search box, then click on Mouse settings or Open
NOTE: If the Type here to search box is not visible, just start typing after you click on Start and it will appearThen click on Additional mouse options
Then under Double-click speed, move the pointer to the left which will slow down the Double-click option
NOTE: Sliding the Double-click speed slider one step to the left is normally sufficient to fix this issue. However, if the issue still occurs, you may have to slide it further.Click OK
