Zodiac kinda sucks because Fincher decided for no reason to take literal grifter bullshit as fact(Richard Graysmith is a hack who literally makes up evidence out of thin air) then also made up a few facts of his own. The whole story of Paul Avery having his life and health ruined is essentially all made up, the guy did have health issues but he wasnt a washed up wreck.

If you make a huge deal out of recreating the tiniest details like having 3 different actors play out the Zodiac killings based on 3 different witness accounts, then just make up stuff like changing dates so an alleged phone call was made on ALAs birthday, you're basically just producing misinformation. The movie is only has an "ambigous ending" because of obligation, any reasonable person who watched it without external knowledge of the case would think "Oh Graysmith solved it, it was Arthur Leigh Allen and they just didnt piece it together in time".