I will try find some time over the weekend to do some testing for this but it does seem to require a bit of a setup to get this started and i just have not found the time.
Just looking at your gif though I do see that the Header is not shown as a parameter in the schema window.
Taking a total wild guess before testing personally I think because your API Action is using GET you should not be passing headers, that is more meant for POST, therefore according to the API documentation on Directus you should rather add your token to your URL parameter.
So according to that you should keep your API Data Source as is, and change your API Action to remove the header and rather add to the end of the URL as a query parameter with
?access_token=PP…
not
?access_token=Bearer PP…
Please let me know if that helps at all, but basically with using GET i really think your need the query parameter and not a header.