Full screen mode is broken in Maschine 3.1 when Windows has DPI scaling on. Size of the displayed Maschine is inversely proportional to the scaling: 200% DPI scaling = Maschine taking 1/2 screen width and height, 300% scaling = 1/3 etc.
Tested in Win11 24H2 26100.3476
EDIT: This is fixed in 3.2