How to disable optional dependency of my dependency?

On my earlier post, I shared that it was impossible to compile psl due to libssl issues under Arch Linux and one of the libraries I use optionally depends on psl crate.
After opening the bug ticket the author suggested to disable the psl but i literally have no clue how to do that.
After searching the web i have tried

[dependencies.mydep]
default-features = false

which doesnt have any effect on anything at all.
How to disable the optional dependencies of my dependency?

I suggest you to check how exactly the optional dependency is enabled.

You can use Cargo.lock to determine all crates that depend on this crate and then check their respective Cargo.toml
It might be that there is more than one crate depending on it, or it is not actually optional