Let $p$ be a proposition and $P$ the collection of propositions. In classical logic, the law of excluded middle holds, and we can model the semantics of this as saying that there is a function $\text{Truthvalue}:P\to \{true,false\}$.
In intuitionist/constructivist logic, the law of excluded middle doesn't hold, and we can model the semantics of this as saying that the function $\text{Truthvalue}$ has a range that doesn't contain only $true,false$. For example, we could have $\text{Truthvalue}:P\to \{true,false, undetermined\}$.
I am having trouble seeing how the (syntactic) formalization of proofs in the curry-howard (CH) isomorphism capture this (semantic) idea. I can see that in the CH isomorphism, LEM doesn't hold by default, but LEM is a syntactic property, and I cannot see how CH can capture the underlying semantics that I just explained.
To be clear, I am referring to the formalization where a proposition $P$ is a type, and a proof of $P$ is an inhabitant of $P$ and a proof of $\neg P$ is an inhabitant of the type $P\to 0$ where $0$ is the uninhabited type. My question essentially is, how can we understand these proof-theoretic (syntactic) notions as capturing the truth-theoretic/model-theoretic (semantic) notion that a truth value cannot just be true or false (but also e.g. "undetermined").