The movie about the cursed child would have been made by 2020.
The movie about the cursed child would be made by 2020.
I want to know which of the sentences will hold good if the movie was to be shooted by 2020.
Neither sentence is grammatical. If the sentences are intended to be uttered now, namely before 2020, then they should be in the future and use "will." If the sentences are intended to be uttered after 2020, they need to be in the simple past or else be part of a conditional sentence. If the implied question is whether "will have been made" or "will be made" is the better choice, I note that this involves the perfect aspect of the verb and that both choices are acceptable though personally I prefer the future perfect over the simple future in this example.