How to set per-monitor scaling on Wayland?

I figured out what was wrong. By default, I had a scaling factor set to handle the HiDPI screen on my laptop. When using Wayland, though, this scaling factor overrides for both screens. The solution was simply to set this scaling factor to 0, which allows both Wayland to pick automatically based on the screen.

Specifically, you need set org.gnome.desktop.interface scaling-factor to 0.

You can do this with dconf Editor, available in the software store: