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You give:

 fn main() {
    let x = plus_one(5);

    println!("The value of x is: {x}");
}

fn plus_one(x: i32) -> i32 {
    x + 1;
}

And then you clarify:

The definition of the function plus_one says that it will return an i32, but statements don’t evaluate to a value, which is expressed by ( ), the unit type.

The clause:

• statements don’t evaluate to a value, which is expressed by ( )

is unclear. ( ) is not a value, but the function is returning something.

Some definitions would help a lot.