Windows 10 - Rate Photos, Find and Sort Across All Folders 

While you are in detailed view turn on the details pane. You'll see a larger view of the image. If that's not big enough click on it to open it in the Photo app. It should appear instantly. Then when you decide the rating just click on one of the stars in the detail pane. You'll have to click on 'Save' at the bottom. You'll have to close the photo app for each photo you open.

You're absolutely right. PNG format also doesn't allow editing of tags. If you want to edit tags for RAW formats like CR2, you'll need an external editor. Unfortunately most of those aren't very user friendly and therefore difficult to use. If your particular use doesn't require them to remain in CR2 format, the Windows Photo app will read CR2 and you can save them to JPG. It should write it back to the same directory as your original file. If the Photo app doesn't read your file, check the MS Store. Get the image reader plugin but make sure it's Microsoft's.

@@Oldguygeek Interesting and thanks for your reply! When I get a chance, I'll look into the reader plugin you mentioned. I'll also try the technique you mentioned for saving/converting to JPG. I'm currently re-looking back into DigiKam, which is free and works in all 3 major platforms. I was considering the Windows Photo app to try to keep things simple. I have some technical skills and use both Windows 10 and Ubuntu 20.04 on different devices.

Sorry, just saw your question. But the answer is no. The rating is part of the file's metadata (internal to the file's header).

Sorry, metatags are inherent in each type of file. PDFs do not have a rating. Can you rename them with a leading 1, 2, or something like that? What's the purpose for rating them? There may be another way to accomplish what you want.

@@Oldguygeek Thanks for looking into it.