From Reedsy:
Character vs. Nature
How do you fancy your chances in a fight against Mother Earth? In this type of conflict, that is exactly what our protagonists are facing. Whether it’s wildlife (Jaws), natural disasters (The Day After Tomorrow), the weather (The Perfect Storm), or a post-apocalyptic landscape (The Road), the antagonists in this type of conflict cannot be reasoned with.
Stories that feature a “character vs. nature” conflict will usually center on a character’s survival.
Freddy and Jason are sources of nature. They have left their human elements behind when they died, and are now physical manifestations of revenge. They're no longer even killing people that had anything to do with their deaths, they just hunt people that end up at the wrong place. Once you have entered their domains, there is rarely any escape.
They can't be the reasoned with, they can't be killed, and they will never stop seeking revenge. They are now eternal elements of Crystal Lake and Elm Street.
In Freddy vs Jason, it's like when 2 weather patterns come together to make a deadly storm. The primary story was still about the kids trying to escape them.
To us as humans, there appears to be a secondary conflict between Freddy and Jason, but I feel you could argue that isn't an actual conflict, as neither Freddy or Jason have any agency. They can't not kill each other. They just don't function that way. As with the storm, they are just 2 elements that mix violently. It's no more a conflict than any story that has rain: the rain is not a conflict between the air and the water vapor held within it, it's just what the laws of the world dictate happens when the air is supersaturated.
(Ok, done editing now. I got more into this than I anticipated...)