Edit: The main role of PM is to decide which features to build, not how those features should be built or how they should work. Someone has to decide what to build, that is the PM, but most PM are not very good at figuring out the best way for those features to work so its better if the programmers can talk to users directly there. Of course a PM could do that work if they are skilled at it, but most PM wont be.
So that we're on the same page, what I think should be PM responsibilities:
If I have a user story: "As a customer I want to purchase a product so that I can receive it at my address" - PM defines this user story as they have insight to decide if such feature is needed.
PM should then define acceptance criteria: "Given customer is logged in When they view Product page Then 'Add product to basket' button should appear", "Given 'Add product to basket' button When customers click on it Then Product information modal should appear" etc - PM should know what users actually want, ie whether modals should appears, or not; whether this feature should be available for logged users only, or not.
How this will work shouldn't matter to PM; these are AC they've defined.
Of course the process of defining AC should involve developers (and QA), because AC should be exhaustive to delivering given feature