> But I don't think that's Wayland's fault - it's up to those apps to upgrade their UI libraries (which might be a monumental task, I'm not sure).
Actually, it is Wayland's fault[0], and arguably Xorg is able to handle it better[1].
Basically, the protocol doesn't currently support sending a fraction as the scale to the application, so whenever you've got displays with DPIs that are not integer multiples of one another, the compositor will scale down on at least one of those displays, causing blur. In Xorg, it is normal for applications to simply detect the DPI of the display they're on and render accordingly. In either case, it requires support from the graphical framework used by the application (eg, Qt applications seem to automatically handle this on Xorg).
I would quite like to replace one of my monitors in a multi-monitor setup with a HiDPI one, but lack of support for this is what's holding me back. I'd be happy enough if Firefox just added support to Xorg for DPI detection[2], though if Wayland gets this working first, I'll probably switch over to that (I've gone back and forth between Xorg/xmonad and Wayland/sway, and I don't really see any other blockers for me).
[0] https://gitlab.freedesktop.org/wayland/wayland-protocols/-/i...
[1] https://www.reddit.com/r/kde/comments/lficfe/wayland_fractio...
[2] https://bugzilla.mozilla.org/show_bug.cgi?id=1679335