Does voltage fluctuation of microcontroller power supply (allowable range 2.5-5.5V) affect the accuracy of analog-to-digital conversion of analog input?

Microcontroller power supply (allowable range 2.5-5.5V) voltage fluctuations, whether it affects the A/D, if your A/D conversion reference voltage is the microcontroller power supply voltage, it will affect the A/D conversion accuracy. If your A/D conversion reference voltage is independent of the fixed, microcontroller power supply voltage changes will not affect the reference voltage changes, it will not affect the A/D conversion accuracy.