This is also what really annoyed me when I tried out Gleam.
I'm waiting for something similar to serde in Rust, where you simply tag your type and it'll generate type-safe serialization and deserialization for you.
Gleam has some feature to generate the code for you via the LSP, but it's just not good enough IMHO.
Multiple of such tools exist and have done for years. Serde isn’t a Rust-core project, and similarly the Gleam alternatives are not Gleam-core.