Dynamique filter on dropdown

Hello Everybody,

I have a question : i'm developping a small interface using powerapps.

To store data, i use a sharepoint list.

I create a form to follow history of data added to sharepoint list.

On this form, i want to create a dynamic search : i explain.

First, i create a dropdown list : on this list i set some column names from my sharepoint list : ex : Author, Status, Country, etc.

On a second dropdown i want to see distinct element based on column choose previously.

Ex : in dropdown1, i select Author, so, second dropdown list must show distinct author who add information to my sharepoint list. For exemple : i can see : Robert, Ed, Toto.

If i select one Author on this dropdown list, now, in my gallery, i want to see all lines added to sharepoint per 'Robert' for exemple.

The problem : on dropdown list : i set column manually, but on second drop down dropdown2, powerapps do not understand column name as param :I set on Items : distinct(Sharepointlist; dropdown1.selectedText.value).

Do you have a solution please ? Thank you.