That's a pretty bold claim.
There's uncountable inputs. It's like trying to accurately predict the weather - chaos theory or something. Emotions are "essentially" gas exchange, but the areas and rate or whatever are not standardized across humans.
I have neither experienced or observed anything about human emotions that indicates they are in any way chaotic, random or unexplainable. We have beliefs, memories and experiences. emotions always use these variables and produce some output. Not only are emotions deterministic, but they are used by any number of people, from spies, to advertisers, to state-level disinformation propagandists to manipulate large numbers of peoples reliably.
So is your claim that 100% of all human emotions are deterministic? That's quite a bold claim don't you think?