Is there any end in sight for the pixel doubling hacks? Why do we even use them any more? Apps should have had plenty time to adapt to higher DPI displays by now, and X11 has supported per display DPI since the 90s and a scale factor on top of this seems obviously wrong.
And for the niche case where you have a big disparity in DPIs of multiple displays + apps that can't adapt to DPI on the fly, scaling up is surely the wrong solution, you should be scaling down no the smaller screen.
I've tried looking a bit into this at one point and my understanding is that it's more a toolkit issue than an app issue.
QT has an option to adapt the size of the widgets according to the reported screen resolution, which seems to kind of work. I don't use that many QT apps, so not sure how this turns out in practice.
However, GTK just doesn't care.
All this is on X11, I hear the situation is somewhat better on Wayland.
And for the niche case where you have a big disparity in DPIs of multiple displays + apps that can't adapt to DPI on the fly, scaling up is surely the wrong solution, you should be scaling down no the smaller screen.