X and GNOME for FreeBSD

Xrandr.

If you just attached a monitor to your computer, such an external monitor or TV via HDMI, you can activate it in GNOME with Xrandr. Just run the utility. If you want to configure it in GNOME, then go to GNOME settings and Display.

% xrandr
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 16384 x 16384
eDP-1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 276mm x 155mm
   1920x1080     60.05*+  60.01    59.97    59.96    59.93  
DP-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 disconnected (normal left inverted right x axis y axis)
DP-2 disconnected (normal left inverted right x axis y axis)
HDMI-2 connected (normal left inverted right x axis y axis)
   3840x2160     30.00 +  25.00    24.00    29.97    23.98  

GNOME Tweaks.

Go to Appearance and change Applications from Adwaita to Adwaita-dark. This will make non-GTK applications, such as third party applications, dark mode as well as the GNOME applications.

% gnome-tweaks