léonie wrote:
The "J" may indicate that you are viewing a photo, that has been imported as a RAW&JPEG pair, and you are currently viewing the JPEG and not theRAW.
These pairs are imported as one photo, and you can switch between the RAW and the JPEG as original photo. To switch between RAW both originals to see the RAW click the EDIT button. That will show controls for handling RAW file.
Well here we go - it's a few weeks since I dabbled more extensively with the beta and this goes to show how unintuitive this system is.
I was just about to post:
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That was my assumption and that the small 'R' on others implied RAW.
However, I have loads of images tagged 'J' - non-system library on non-startup internal drive imported with the beta a few weeks ago.

None are now offering the ability to use the 'RAW' - I need to find the source images to check they were catually JPEG/RAW pairs, but I normally shoot with both settings unless I'm running low on space and need a few more shots and switch to JPEG only. When I select the image thumbnail for such an image the 'Use RAW as Original' is always greyed out:

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Reviewing your post above, struggling to find the Edit button - because it's unavailable with a selected image in thumbnail mode only fullscreen mode - when I try the same menu fullscreen, same issue unless Edit selected:

With Edit, the dropdown menu or contextual click on teh image allow you to select RAW:


Selected and i get a small R:

The interface has so many hidden features or things which only work in specific ways (so you think it's not available at all) that you really get the feeling that it has only been internally tested with a very small number of images, otherwise such inefficiencies would have been apparent.
So if I have 500 RAW/JPG files imported, do I have to choose 'Use RAW as Original' for every single one!!! Is there no global setting? Not that I can see....I've tried selecting several Photos in thumbnail mode but no the option is still greyed out.
Even then - we probably would not only want to be using RAW or only JPG - what is required is the ability to easily switch for individual images or groups of images, plus a preference on Import to choose which to used initially for that batch of Photos.