The amount of solar energy that a solar panel can pick up on a cloudy day depends on a variety of factors, such as the type and quality of the solar panel, the intensity and duration of the cloud cover, and the angle and orientation of the solar panel.
In general, solar panels can still generate electricity on cloudy days, but the amount of energy produced will be significantly lower than on a sunny day. According to some estimates, solar panels can still generate between 15% to 25% of their maximum rated power output on a cloudy day, depending on the factors mentioned above.
It's also worth noting that some types of solar panels are better suited to generate electricity in low-light conditions, such as monocrystalline solar panels or thin-film solar panels. These types of panels can be more expensive, but they may be worth considering if you live in an area with frequent cloud cover or other low-light conditions.