Using i2c network in the hypothetical application at the page "real time application tutorial"

At the page “real time application tutorial” can we use i2c network in place of fieldBus network in hypothetical application? I want to implement this application on avr atmega32

Sure - its just an example. An atmega32 is quite a small device (limited RAM) though. Do you need an OS at all?

I just want to exercise programming real time application with freertos. and i found this hypothetical application a good & complete example for exercising. I have both atmega32 & stm32f103c8t6(blue pill board). Which of them do you suggest me for implementing this application on?

Any of them should be fine if you are just using them for learning. You may also find these tutorials useful for learning FreeRTOS.