valid code that rust fails to compile

fail.rs

#![allow(dead_code)]

struct Input<'a, 'b> {
    a: &'a i32,
    b: &'b i32,
}

struct Output<'a, 'b> {
    a: &'a i32,
    b: &'b i32,
}

trait MyTrait {
    fn run<'a, 'b>(&self, i: Input<'a, 'b>) -> Output<'a, 'b>;
}

impl<F> MyTrait for F
where
    F: for<'a, 'b> Fn(Input<'a, 'b>) -> Output<'a, 'b>,
{
    fn run<'a, 'b>(&self, i: Input<'a, 'b>) -> Output<'a, 'b> {
        self(i)
    }
}

fn main() {
    // I want to create a Box<dyn MyTrait> from a closure, but this doesn't work
    //
    let _doesnt_work: Box<dyn MyTrait> = Box::new(|i: Input<'_, '_>| Output { a: i.a, b: i.b });

    // Therefore I tried to help the compiler infer the correct type:
    // let _dyn_fn: Box<dyn for<'a, 'b> Fn(Input<'a, 'b>) -> Output<'a, 'b>> =
    //    Box::new(|i: Input<'_, '_>| Output { a: i.a, b: i.b });

    // So now I have a Box<dyn Fn(Input) -> Output> which implements MyTrait,
    // but how do I turn it into a Box<dyn MyTrait>?
}

Someone on Discord found how to make it compile: https://discordapp.com/channels/442252698964721669/443150878111694848/793854339113680926

#![allow(dead_code)]

struct Input<'a, 'b> {
    a: &'a i32,
    b: &'b i32,
}

struct Output<'a, 'b> {
    a: &'a i32,
    b: &'b i32,
}

trait MyTrait {
    fn run<'a, 'b>(&self, i: Input<'a, 'b>) -> Output<'a, 'b>;
}

impl<F> MyTrait for F
where
    F: for<'a, 'b> Fn(Input<'a, 'b>) -> Output<'a, 'b>,
{
    fn run<'a, 'b>(&self, i: Input<'a, 'b>) -> Output<'a, 'b> {
        self(i)
    }
}

fn new_my_trait(i:impl for<'a, 'b> Fn(Input<'a, 'b>) -> Output<'a, 'b>) -> impl MyTrait{
    i
}

fn main() {
    // I want to create a Box<dyn MyTrait> from a closure, but this doesn't work
    //
    // let _doesnt_work: Box<dyn MyTrait> = Box::new( |i: Input<'_,'_>| Output { a: i.a, b: i.b });
    let _doesnt_work: Box<dyn MyTrait> = Box::new( 
        new_my_trait(|i: Input<'_,'_>| Output { a: i.a, b: i.b })
    );
    

    // Therefore I tried to help the compiler infer the correct type:
    let _dyn_fn: Box<dyn for<'a, 'b> Fn(Input<'a, 'b>) -> Output<'a, 'b>> =
        Box::new(|i: Input<'_, '_>| Output { a: i.a, b: i.b });

    // So now I have a Box<dyn Fn(Input) -> Output> which implements MyTrait,
    // but how do I turn it into a Box<dyn MyTrait>?
}