Thank you for the sample file.
It looks like HDR-PQ mode was enabled for this file, found in the red Canon camera menu.
Photo Mechanic cannot currently display the embedded preview filetype generated by the HDR PQ mode. Our developers are aware of this and we hope to include a fix for this in the future.
A workaround is to convert these CR3 files to DNG files using the
Tools--Convert RAW to DNG option. You'll need Adobe DNG Converter (
https://helpx.adobe.com/camera-raw/using/adobe-dng-converter.html) installed if it is not already.
Once it is, use the "Pick DNG Converter" button in the Convert RAW to DNG window to select the install location of Adobe DNG Converter.
With Adobe DNG Converter open, under the Preferences section, select the "Change Preferences..." button.
In the Preview/Fast Load Data section, change the JPEG Preview: dropdown option to "Full Size".
You'll need to convert at least one image directly in Adobe DNG Converter for it to work properly with Photo Mechanic.
You can then go back to
Tools-->Convert RAW to DNG in Photo Mechanic, then select the 'Convert' button.
Edit:
A different workaround is to open the affected CR3 files in your photo editing program and have your photo editing program export new JPEG files that have the same filename as the CR3s to the same folder as the CR3 files.
For example: IMG_1234.CR3 and IMG_1234.JPG
When the CR3 and JPG file are in the same folder, and that folder is open as a contact sheet in Photo Mechanic, Photo Mechanic's RAW+JPEG mode with combine the two files into one thumbnail in the contact sheet and one preview in the Preview window.
You can toggle RAW+JPEG mode off/on using
View-->Combine Images or Command-J on macOS and Ctrl-J on Windows.
In Photo Mechanic's
Preferences-->Launching, you can choose the "Edit the RAW photo" option for "When in RAW+JPEG mode, editing a photo will:" to send the CR3 file to your editing program instead of the JPEG.
