How can the digital GPIOs accept the analogWrite() function?
When you use analogWrite() the pin still gives output as digital signal but uses Pulse Width Modulation (PWM) to represent an analog signal.
You can refer this for more information on how PWM works:
https://www.seeedstudio.com/blog/2020/06/16/basic-electronics-pulse-width-modulationpwm-and-arduino-applications/