Preview does not open JPG photos

Apple's Preview universally accepts .jpg, .jpeg, jp2 or their uppercase variants. If you perform a Finder Show info (option+cmd+i) on one of the images that Preview won't open, what does it say about the Kind?

Did you move these images directly from some cloud service to that external drive? For instance, files on Microsoft's OneDrive are encrypted and without the macOS OneDrive application to remove that encryption, you could have images that are encrypted and no Mac application is going to open them.

Hopefully, these are not encoded jpeg xl (*.jxl) images renamed to .jpeg.

Apple's iCloud does not encrypt images, so a straight drag and drop to your external drive should have not changed the images in route to your external drive. However, if the images were originally on another cloud service that did encrypt them, Apple's iCloud would simply pass along that restriction to your external drive.

Can you open any of these images with Graphic Converter 12, or by clicking once on the image and pressing the space bar to open a Quick Look view? What specific camera make and model took these images?

Do you happen to have the free ExifTool installed, so you can look at the internal image metadata?

Try changing the file extension to JPEG and default app to Preview in the Get Info section by Right Clicking on the file

What Format is the My Passport drive?

As a test does GraphicConverter open them...

https://www.lemkesoft.de/en/products/graphicconverter/

http://www.lemkesoft.com/