Was ist der Unterschied zwischen who was it that broke the window? und who broke the window? ?Du kannst auch einfach Beispielsätze geben.

They have the same meaning, the only difference is that "Who was it that broke the window" has a predicate nominative/subject complement while "who broke the window" doesn't.
here are examples for predicate nominative/subject complement:
-you are nice
-I am a student
-That bird is small
-the dog is large
A predicate nominative/subject complement is a noun that comes after a linking verb. Basically it's describing the noun through a verb. So you are pretty much saying that Something is Something else (the something else is the subject complement)
Sorry for this being long, but I hope it helps!