I’m going to give a slightly off-target answer to this: I ran ‘darktable-cltest’ before I saw your reply; the result is in the screen shot. The lack of file ‘libOpenCl.so’ bothered me greatly 2 days ago when I was reading the manual. I couldn’t understand how dt was able to activate OpenCl ever in the absence of this file - but it does and the file is definitely not there: I asked Thunar to search for the file across the whole of my PC.
Screen shot:
Now I’ll run dmesg:
Huge amount of output to terminal: where should I be looking ?