I have a dirty workaround.
I put in the Convert to binary data action (from File actions), using something invalid, so it fails updating the same variable used with the sharepoint action.
However this works, so the flow will actually run, I set the input to the "Convert to binary data" action (from File actions) to the same sharepoint file, and set the "on error" to just continue (it will not be able to convert this file).
This fools the sharepoint version of convert to file without errors.