It took a long time for Canon CR3 raw format to be supported by darktable because, although the format itself had been reverse engineered, there was a fear from the developers that it was covered by a patent and that they risked a lawsuit by integrating it in DT. IIRC, they had attempted to contact Cabon legal to obtain some sort of waiver, without success.

I'm fact I'm not sure how that saga ended and CR3 support was finally added a few years after the release of the Canon mirrorless cameras that output CR3.