The sentence follows the pattern "If + had + past participle, ... would have + past participle", which grammar calls the third conditional. This structure is only used to describe a past that did NOT actually happen, an imagined alternative to reality, so whatever sits in the "if" clause must be false in real life.
- The actor will certainly sponsor his next movie: this talks about a future certainty, but the given sentence only imagines a past that never occurred; it says nothing definite about what will happen going forward.
- His latest movie was a commercial success: this directly contradicts what a third conditional tells us, since the "if" clause describes something that was not actually true.
- The actor made enough money from his latest movie: this can only be true if the movie really was a commercial success, but we already know it was not, so this cannot be true either.
- His latest movie was not commercially successful: this is exactly the real-world fact that the third conditional points to, since the imagined "if it had been a success" case never actually happened.
Because "if X had happened, Y would have happened" always means X did not really happen, the true statement here is that the movie was not commercially successful.
Let's summarize:
- "If + past perfect, would have + past participle" describes an unreal, imagined past.
- Whatever sits inside that "if" clause is understood to be false in reality.
So the only statement definitely true is that his latest movie was not commercially successful.