For Wayland:
Enable the experimental fractional scaling feature:
$ gsettings set org.gnome.mutter experimental-features "['scale-monitor-framebuffer']"
For Xorg, @pux maintains the mentioned Ubuntu patches in a couple custom packages. Install both which will replace mutter and gnome-control-center:
sudo pacman -S mutter-x11-scaling gnome-control-center-x11-scaling