Hey moenk,
Even i was facing same issue and Uipath was showing the message like for New tab browser won’t support when i try to find elements, then i tried to navigate url in same browser which i was trying to download file just to find the Save as in Downloads window.
After immediately started recognizing the Save As file popup and once i click on Save as immediately i am closing the browser since no more required.
If your downloads popup window is opening with New tab browser then you can follow above method.
Hope this will help you…