Is there a hierarchy on Apple devices for extending screens?

I have a few Apple products, and would like to know the title question.

Let me explain:

I have a iMac (from 17) with the latest software update, and I recently bought a MacBook Pro M1 Max.

I'm able to extend screen from iMac -> MacBook, but not the other way around, as I would like.

(In short, using my iMac as a second screen).

I can extend mouse and keyboard from MacBook -> MacBook, but not extend screen (I also have a MacBook from 19).

I'm able to extend screen from MacBook to iPad.

So as of right now, in my testing, you can extend down but not up, and extend mouse/keyboard to same level:

iMac

Macbook

iPad

I've tried searching around for the question, unfortunately I haven't stumbled upon something useful.

It could also just be that my other gear is older and therefore cannot be used in this sense, but I would like to know more :)

Thank you

Niclas