How to get the encoder position while the rotary motor is moving
While your delay() function is running, you won't be able to read any data. Suggestion is to use interrupts, which basically guarantee that whenever your pin state changes (low edge, high edge, or any change, feel free to select it), some action will be performed. This action can be reading your encoder position.

Read about it here https://www.arduino.cc/reference/en/language/functions/external-interrupts/attachinterrupt/

I am sure it will answer all your questions, it is quite well documented