cr3 is listed in the parsed extensions (they are all lower case, adding uppercase not an option), but the browser doesn’t see the .CR3 files, just shows the .JPG I translated elsewhere. This is via launching the desktop flatpack version 5.8 in ubuntu/pop!os 21.04.
Under flatpack I don’t see anything like a tree structure with an options file to delete. I reinstalled in case it would do it.
Fwiw I also note /usr/share/mime/image/ files like x-canon-crw.xml and x-canon-cr2.xml, but no cr3 version.