What is the difference between the CALENDAR and CALENDARAUTO

The first level of difference with the CALENDARAUTO and the CALENDAR in Power BI is that:
CALENDARAUTO had scanned the entire model automatically and brought back the date table with all dates found in the model.
While for CALENDAR, you have to specify the start and end dates for the date table in person.

CALENDARAUTO is helpful if you want to create a date table that automatically includes all the dates present in your model.

The CALENDARAUTO function can cause a circular dependency issue in your model, particularly when creating relationships between tables that have date columns or when using a calculated table.