Comment 6 for bug 1528319

@Kai: You can set per-monitor scaling by setting org.gnome.desktop.interface scaling-factor to zero, and then Wayland figures out the scaling automatically. But it only works for apps that support Wayland directly (like nautilus), not for apps that run under XWayland (like chrome and firefox and most other apps as well), so it's a bit pointless at the moment. There's some info here: https://askubuntu.com/questions/875832/how-to-set-per-monitor-scaling-on-wayland

The page https://wiki.gnome.org/HowDoI/HiDpi talks about HiDPI support via the org.gnome.settings-daemon.plugins.xsettings overrides setting. I think it says Wayland detects monitors above a certain resolution as HiDPI and applies the override scaling factor you set (eg of 2) just to those monitors, but I haven't tried it. (My guess is it also doesn't work with XWayland apps). And https://bbs.archlinux.org/viewtopic.php?id=221742 discusses issues when trying to use this setting.