4k laptop monitor and 4k external monitor, XFCE4 2x works perfectly I also use 2 different resolutions without problems KDE plasma gives you fractional scalin

4k laptop monitor and 4k external monitor, XFCE4 2x works perfectly I also use 2 different resolutions without problems KDE plasma gives you fractional scaling I've heard Wayland supports different scalings on different monitors, but I'm on Xorg so I can't say if it works