Removed ifdef DisposeOf and added default Result for createinstance, both raise warnings in Delphi 12. The former's function is now depricated and the latter case was likely masked in previous compiler versions.

Quick.RTTI.Utils.pas

@@ -88,6 +88,7 @@ var
   rmethod: TRttiMethod;
   rinstype: TRttiInstanceType;
 begin
+  Result := CreateInstance<T>([]);
   rtype := fCtx.GetType(TypeInfo(T));
   for rmethod in rtype.GetMethods do
   begin

Quick.Threads.pas

@@ -685,7 +685,7 @@ begin
   try
     for obj in FQueue do
     begin
-      if TypeInfo(T) = TypeInfo(TObject) then PObject(@obj){$IFNDEF FPC}.DisposeOf;{$ELSE}.Free;{$ENDIF}
+      if TypeInfo(T) = TypeInfo(TObject) then PObject(@obj).Free;
     end;
 
     SetLength(FQueue,0);