Hi, can you provide an official source for this title?

As far as I can tell, the Chinese artwork, website and most sources use "愤怒的小鸟." I however do not have access to the opening credits. It's also worth noting that the change to "愤怒的小鸟大电影" was made by a former mod (Marr).

I agree that "愤怒的小鸟" should be the official zh-CN title, as it's used:

1. on all promotional materials (see google images),
2. on tickets when it was on theatres,
3. by streaming platforms (1, 2),
4. and it can't get more official than the release notice and permit. If you are curious, yes, the official titles in release notices can sometimes include "大电影", just not this one.

The title in the opening credits sadly wasn't localised. "愤怒的小鸟大电影" can be found in news and articles to disambiguate the movie from the game, but it's more often written as "《愤怒的小鸟》大电影" — notice there're guillemets suggesting what's inside is a proper title. It's also a more direct translation of "The Angry Birds Movie", so the likely result if one were to consult any translation programme for verification.

I have changed the title. Thanks.