Venus planetary dynamo
I wonder why it has practically no magnetic field.
Fundamentally two reasons probably.
Venus doesn't rotate rapidly enough and the thermal gradient in the Venusian mantle is less due to the high surface temperature.
Both conditions which would limit mantle flow to produce a dynamo, the source of Earth's magnetic field and possibly Mercury's.
Also there is no way to tell (from orbit) if there were a planetary dynamo because the surface is too hot for natural ferromagnetism to last like it has on Mars.