HI, I am Dave, I will help you with this.
In Windows 11 currently the Calendar will only display on the monitor you have set as the primary display, there is no setting, method or registry hack to get the calendar to display on the other monitors.
The best option is to open the Feedback Hub (Windows Key + F) and report this lack of functionality in Widows 11 to their developers there, the more people that request an option, the morel likely they are to add that as an option.