No spin, other than once per year, also means no magnetic field to protect its atmosphere. It’s probably more like Mars than Earth; a near-vacuum desert planet.
Maybe no spin, but I doubt that a magnetic field has much to do with whether there's any atmosphere, either there, or on Mars, or Earth for that matter.
Venus is known not to have a magnetic field. The reason for its absence is not at all clear, but it may be related to a reduced intensity of convection in the Venusian mantle. Venus only has an induced magnetosphere formed by the Sun's magnetic field carried by the solar wind.
Venus has the most massive atmosphere of the terrestrial planets, which include Mercury, Earth, and Mars.