How to define a microcontroller pin as open collector or open drain??

https://www.microcontrollertips.com/what-is-an-open-drain-faq/

I have understood the fundamental theory of open collector and open drain configuration. But the problem is How to define/make a micro controller's pin as open drain??Does any pin of a micro controller can be used in open drain configuration??

2. If i define a GPIO pin as an input pin, Can I use this pin in open drain configuration?
3. Does it mandatory to define a pin...

How to define a microcontroller pin as open collector or open drain??