Your camera model is new. For CR3 files darktable uses LibRaw and not Rawspeed, so you will need to wait for next version around Christmas.
When you see your camera name here, then it is supported with color matrix and the right border crop.
What you can do meanwhile is to upload free sample CR3 files to https://raw.pixls.us/ including RAW and cRAW.
More details here Canon R8 Support · Issue #14549 · darktable-org/darktable · GitHub
And here Canon EOS R50 Noise Profile · Issue #14574 · darktable-org/darktable · GitHub
With that said darktable opens R50 raw files, but with wrong color matrix and wrong crop.
144px crop from left side, 40px crop top and 0px crop right seem to be better than 168px, 52px and 24px. You will see the full image if you go to the module raw black/white point and in the hamburger menu click passthrough.
About Lensfun then. No one has added your camera there. It is really a simple task. You need to create the following:
<camera>
<maker>Canon</maker>
<model>Canon EOS R50</model>
<model lang="en">EOS R50</model>
<mount>Canon RF</mount>
<cropfactor>1.613</cropfactor>
</camera>
Use your OS search feature to find mil-canon.xml