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"The whole object aimed at white will become very dark", because the automatic exposure program always treats the object as gray, so the exposure automatically set at this time is too small, so the result is that white is not enough (on the contrary, for black objects, it will be overexposed and black will turn gray)

Knowing the reason will solve it. For white (it should be said that light color) objects, exposure should be increased on the basis of photometry (that is, automatic setting), and more straightforward should be increased. For example, snow scenes basically need to be increased by two levels (semi-automatic, through the exposure compensation function, the general camera compensation range is -2~+2, with positive and negative levels. Full manual mode is recommended, with higher degree of freedom).

As for "the bright yellow that can't shoot the sun is always white", besides the actual sunshine situation and exposure may be wrong (using automatic mode in the sun, the exposure may be insufficient), there may be a problem with the white balance setting. Try to change the shooting.

Good luck!