If you created this map before adding Saturday and Sunday as Workdays, you will need to adjust the calendar options for the specific file.
1. With the file open, open the Task Pane and then click on 'Calendar & task option's.
2. Add Saturday and Sunday as workdays.
3. Reopen the Gantt Chart and you should now be able to drag tasks to Saturdays and Sundays.
As soon as I delegate a task to a resource, i believe it does take the calender for the resource.
However, The weekend is still not counted, so you may be right
I have created maps after setting custom workdays in [File > Options > Task Info]. I have restarted the software, but it didn't work. New maps are always created with (sat/sun)day as weekends. But your method has worked, thank you so much. Since we don't create too many maps, this is an acceptable solution. MindManager is definitely a real mind manager with no close alternative. Thanks to all of you
This video shows how to activate Saturday and Sunday for the task info.