Canon Raw Files with Big Sur and Preview

Works for me and R5 and R6 are listed in System report's raw support and it works for QuickLook and 3rd party apps like GraphicConverter (also LibRaw should now support R5 and R6). Some people in AFAIR Photos forum have had similar weird trouble (R5 and R6 were listed but QuickLook did not open them) but in the end the raw support was somehow updated.

Quick Look (spacebar) works on. a single image from the Finder. Use the arrow keys to advance to the next image. Preview has a View menu > Contact Sheet option that allows one to open several selected, or a folder of images and view them as if on a light table.

There were issues in macOS 11.2.1 where the R6 was shown to be supported by Apple's camera RAW, but some of us could view R6 RAW images, and others could not. Still don't know why, and hope macOS 11.2.2 resolves that issue.

Is R6 listed in your system report? Can you double-click to open .cr3 to Preview or open it from Preview?

https://discussions.apple.com/thread/252409677?answerId=254550850022&page=1

That raw support should have been included in 11.2.1 but somehow it didn't properly at first install then for some systems then.