Canon 600d outdoor portrait shooting, aperture priority, evaluation metering, forced flash, overexposure, what's the matter?

It's better to use spot measurement for portraits, so that the exposure of people will be more accurate and the interference of the environment will be less. Especially suitable for low light environment at night. The brightness of the environment will affect the exposure of the characters after you use the evaluation. Soft light effect under shading, small contrast between light and shade, and no overexposure. For reference.