Thank you!
You’ve obviously gone much further than I, and I fear you may be right that a completely dependable, fleshed out solution will be a while yet. Again, I may land on a compromise that works for me, but as you can tell, I’m very excited having anything that even gets close. The Photos app is just the top layer for convenient access, but being able to stay in Darktable and still reap most of the benefits of HDR reproduction is a revelation to me. One can always change the settings and do a new export in bulk somewhere down the line.
PQ seems the better choice for professional work that warrants something approaching absolute control, but as you noted, it doesn’t appear to work as well for now. It seems likely the relative nature of HLG is a better fit for Apple, given that they still do their own thing on an OS level, across different hardware.
By the way, does anyone get why the Adobe stuff looks so different (to me: awful) out of the box? I’m talking a basic import in Lightroom, HDR enabled and some auto adjustments. The overly bright and overly saturated highlights looked like over-processed photos from a smartphone. The gain map thing seems clever, but I haven’t yet seen results I like from it.