@Pascal_Obry , @houz - thanks!
I had looked for the “color/in” and “color/out” folders in the darktable config folder ($HOME/.config/darktable), because I wanted to use a custom camera input profile, but I couldn’t find these folders in any of the darktable configuration folders. But it turns out that hovering over the “select profiles” boxes does show two possible places to put these folders, and creating the folders by hand worked just fine - maybe these folders always needed to be created by hand and I just forgot.
Personally I like to keep all of my ICC profiles in one folder. So rather than make duplicate copies of selected profiles just for darktable to use, I softlinked “color/in” and “color/out” to that one folder.
Regarding the system monitor profile, thanks! It’s nice to know one can set the display profile “by hand” for darktable, and I just hadn’t found the right icon to click.
“Automatic color management” software make me nervous as in the past I’ve had three such softwares silently (no user warning) install the wrong monitor profile: oyranos and colord both pulled an EDID profile and installed it as the system monitor profile, and some command line utility (maybe xcalib?) installed sRGB (some version of sRGB that it got from somewhere) as the system monitor profile.
Maybe these softwares have changed their behavior since the last time I had them installed on my computer (several years ago), because with something as important as installing a system monitor profile, it’s crucial that the user know what software installed which profile as the system monitor profile.
I used to not install any system monitor profile at all, but now I use ArgyllCMS “dispwin” just to thwart the possibility that some “automagic color management” software might be trying really hard to make color management “easier” by installing the wrong system monitor profile for me. But I also try to keep all such software completely off my computer.