Higher pressure on sunny days or higher on cloudy days?

Sunny day.

Generally speaking, in the same area, the air pressure on sunny days is higher than that on cloudy days, and the air pressure in winter is higher than in summer. Atmospheric pressure is related to air density. Water vapor is less dense than air. On cloudy days, there is more water vapor in the air, so the air pressure becomes lower.

Atmospheric pressure is the atmospheric pressure acting on a unit area, which is equal to the weight of a vertical column of air extending upward to the upper limit of the atmosphere per unit area. Pressure is related to altitude, temperature, and other conditions. Generally speaking, it decreases with increasing height. In the horizontal direction, atmospheric pressure differences cause air to move.