@dkf said in I've got a new monitor!:
You also see some of that sort of thing when you've got a window mostly on a low DPI screen but partially on a high DPI screen, and I can't remember which app it was (and can't check now) but there was at least one that rendered part of its window quite differently on high DPI which was weird.
My newest Mac is from 2011. SandyBridge + Radeon HD5760. So your mileage may vary if you use something less ancient. In my case, when I move a window, the destination screen shows the window drawn translucently at the resolution of the destination screen, however, if I stop it midway, only the half of the window that's on the source screen is shown.
GNOME + Wayland gets it totally right: each half of the window is shown at the screen's native resolution. However, most apps that matter on a daily basis (Chrome, Sublime, Firefox, JetBrains IDEs) are not Wayland-native, and thus upscaled from bitmaps (read: ugly). That's why I'm using Xorg and scale=200% on all displays.