Just create date parameter and then add extension api in dashboard.
can you please share the .twbx?
select "All" in the parameter instead of "List" and it will show all the available option. In order to see the new values in the parameter it seems like you have to select some value in the parameter. I would expect the list to refresh as soon as data source is refreshed in Tableau. It also does not have "All" as one of the values in the list for string data type.