KB10668 - How can I store/read the configuration for in-memory (non-persistent) layer? I tried to use the project file, but a non-persistent layer is ignored.

This is logical. Project files contain no knowledge of how to recreate a non-persistent layer. You must add such action on your own.

For example:

procedure TfrmMain.createLayerAndSaveConfig;
var
  ll : TGIS_LayerVector ;
begin
  ll := TGIS_LayerVector.Create ;

  ll.StoreParamsInProject := False ; // DK8 only
  ll.ConfigName := 'mylayer.ini' ;
  ll.Params.Area.Color := clRed;
  ll.WriteConfig ; // copy layer parmeters to configuration file
  ll.SaveAll ; // to save all changes including ini file
end;

procedure TfrmMain.createLayerAndReadConfig;
var
  ll : TGIS_LayerVector ;
begin
  ll := TGIS_LayerVector.Create ;

  ll.StoreParamsInProject := False ; // DK8 only
  ll.ConfigName := 'mylayer.ini' ;
  ll.RereadConfig ;

  if ll.Params.Area.Color = clRed then begin
    ShowMesssage( 'Bingo!')
  end ;
end;

Also, you can use TGIS_Viewer.OnLayerAdd & OnLayerDelete to automate such process.

DK9 Note
With the introduction of DK9 TGIS_LayerAbstract.StoreParamsInProject has been removed. Parameters will be read write form the .INI file if such file exists. If you want to create a new .INI file  just create an empty text file just before calling WriteConfig method.