Restarting Darktable seems to have fixed it. I successfully importd a raw image from my Canon, and after a struggle, got the setting done for Canon G7x Pro Mk II. That sorted out the image. Can I tell the software to always do that automatically?
My image needed cropping, straightening, and parallax correction. The cropping goes easily. The straightening is much too sensitive, and worse of all, after I do anything, if I touch the top of my mouse everything gets way out of whack. So I backtrack in 'history' and try again.
Another annoying thing is as I'm using Darktable, it grows in size, so I can't see it all on my (already too small) screen. Not sure why it does that - eventually I can fix it, but then it tries to do it all over again.
I'm going to keep at it, as I expect eventually I'll be familiar with it, but right now Lightroom seems much more intuitive - and the controls are always in the same place.