I use whatever package is shipped by arch, so I think I'm fairly up to date.

I did look a bit into this at one point, but I've found that it's mostly QT apps which work fine with different scaling (telegram comes to mind). GTK apps never did, but I admit I never went too deep in the rabbit hole. Didn't know there was supposed to be some kind of daemon handling this. I do run xsettingsd, but for unrelated reasons. I'll have a look if it can update things.

In any case, except for work, I always used everything at 100% and just scaled the text as needed, which worked well enough.

> I've bothered to look at (and play with) what's actually going on under the hood, and the underlying systems totally expose per-display scaling factors...

Would you care to go into some details? What systems are those and how do you notify them there's been a change?