Open the box calendar in which the events from other calendars should appear (the target calendar).

Below the calendar, you will find the “Add calendar” button.

A dialog opens in which you enter the link to the source calendar. You can get this link directly in the source calendar by clicking the share button.

Confirm the selection, and all events from the source calendar will immediately appear in the target calendar.

You can embed as many calendars as you like into one box calendar.