@mk
Image brightness depends on several factors: lens, sensor sensitivity, exposure time, gain, and post-processing. The photosensitive ability of lens and sensor is constant in the set state, and the post-processing is ugly because it will damage the details of the image.
In AE mode, adjusting aetarget will automatically adjust the exposure time and gain to achieve the purpose of adjusting the brightness of the image.
In ME mode, the exposure time and gain need to be adjusted manually. Because you want to control it manually, there is no auto adjust and no target.