I'm not sure if that's a great example. What kind of errors could ShouldBindQuery return?

I would assume Axum returns a bad request error for you when query parsing fails, but if you do want more control over how the error is handled, you can change the parameter type to Result<Query<bool>, QueryRejection>, and the type system itself documents precisely what errors you can match against.[0]

[0]: https://docs.rs/axum/latest/axum/extract/rejection/enum.Quer...