I have a 4k laptop display and dual 1920x1200 external monitors, one rotated vertically so emacs can have a million lines in view. Font scaling is set to 200% on the laptop display and 100% on the externals. This is in Gnome under Ubuntu 22.04.2 and using Wayland, GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.30, cairo version 1.16.0) of 2022-01-24, modified by Debian.
Expected and desired behavior: When I move a window from the laptop to the external monitor, as the cursor crosses over, the window shrinks to the external monitor's 100% scaling, and vice versa when I cross back. Gnome-terminal and nearly all other windows do this. The windows have approximately the same physical size on the two monitors, but of course look better on the 4k display.
Emacs behavior (undesired): The window size changes by a factor of 2 (counted in pixels, not linear measure), but the font does not change, so it looks HUGE on the external monitor, and the width in characters is unusably small.
I have searched for this problem but have not yet found it here or on other forums, nor in the Emacs Wiki. I see lots of ways to set the default font or change the font manually, but I want it to work automatically. I also want it to work for everyone, not just those of us making a fancy special hack or setting, though that would be the first step.
I'm a little surprised this hasn't been dealt with already. Retina displays have been around forever and nearly everything else "just works"...what am I missing? Is this a Wayland issue and it works on X.org? I'll switch back if so, though I think we'll all be dragged into the Wayland universe, eventually.