Thank you @Arkshine! I think I understand how to pass actions in a glimmer component in general. However the route-action helper moved along the route hierarchy to invoke an action that is not declared in local scope. So you could just declare it on the component, e.g.:
{{route-action "showLogin"}}
{{route-action "showCreateAccount"}}
{{route-action "composePrivateMessage"}}
I could just work on the template, care less about the invoked logic because it’s auto-magically passed in (from my point of view :). Which I liked, but I don’t understand if that was ever best practice and if/how I would have access to that now in a glimmer component.