Of course not everyone will have seen it and totally abandoned their beliefs, but I do feel that if any Christians are looking for more answers, even if they hurt, it can absolutely provide context and give a deeper understanding of the origins of religion.
Part 1- https://youtu.be/BzMqlsAGL14
Part 2- https://youtu.be/SvoUTea092k
Part 3- https://youtu.be/k7eptE9KRlM
Horus Ruined Christmas - Erhmagerd! - https://www.youtube.com/watch?v=s0-EgjUhRqA
Astrotheology, whoop a doop. It doesn't undermine anything for that to be true.
As for "Constantine broke da Church." Whatever, man. Even if you're an anti-Papal conspiracy theorist, Roman Catholicism is not even the sole representative of the Christian faith. You have the issue that Eastern Orthodoxy and Coptic Christianity also exist as well as all those Nestorians who went over to India and China to deal with in your speculation before you can make it convincingly. Constantine's only actions were legalizing Christianity (before that, people got thrown to feed lions supposedly...) and calling for a council so Christians would stop all the bickering between Arianism and Trinitarianism over the best way to interpret the fact the Bible seems to talk about Jesus like a Divine being. Basically: Is "he's God's right-hand dude" or is "He a full personal manifestation of God Himself?" Did Constantine have nefarious ulterior designs? Maybe. Maybe not. It's entirely possible he wanted to do some kind of Mithraism thing where he made himself into the head of the religion eventually. But it really doesn't matter though since he died. And then later Julian the Apostate came and re-paganized for a few years a couple of decades later so it undid anything that was planned there. Christianity wasn't even made the state religion until Theodosius came along 40 years later.
Whether or not you subscribe to them, religions are touching similar psychological mechanisms. You can make a reasonable that a Divine entity would work with mechanisms like that. Why not? Because some skeptical prick might say "oh it's all just self-driven natural forces?" That sounds like a personal interpretation hangup not a disproof of any Divine entity.
All in all nothing this film claimed really was all that shocking when analyzed rationally and historically. It doesn't really undermine anything meaningful in Christianity. At best it's just another angle with which to interpret the historical evidence.