function SortByName(const left, right: TTypinfoTreeview):Integer; // Analog dazu SortByNameDesc
begin
  if left.Modell>right.Modell then
    Result:=1
  else if left.Modell=right.Modell then
    Result:=0
  else
    Result:=-1;
end;

TTreeviewService = class(TinterfacedObject, ITypTreeViewInterface)
private
  ...
  fSortFunction: TComparison<TTypinfoTreeview>;
  ...
end;

procedure TTreeviewService.SortByModell;
begin
  if fSortFunction=SortByName then // Hier kommt E2035 not enough actual parameters
    fSortFunction:=SortbyNameDesc
  else
    fSortFunction:=SortbyName;
end;