In my experience, the majority of documentaries have, at a minimum, a major slant or bias towards a particular message or outcome and will usually hide that bias and present themselves as objective truth. They should be consumed as entertainment and probably shouldn't shift your priors very much on the state of the world.

Some of them are probably exactly what they convey themselves as (relatively unbiased, informative, etc.), but if you are not already an expert in the topic, you can't tell the difference between those ones and the ones that are basically propaganda.