I just discovered A.I Gigapixel by Topaz Labs.
Below a small size 640×512 pixel preview image, click on it for a 400% resize of the original image (17,280×13,824 pixels). It’s a big file and is slow to display so best not attempted on a slow internet connection, once loaded click on the magnifying glass to display at full resolution. The software will go up to 600% enlargement if desired. Amazing technology!.