The data backup function in the Android calendar app applies only to calendars labeled as "In-App Calendar" when edited within the app.
As a result, data related to Google Calendar (linked to a Gmail account) cannot be exported using the app’s backup feature.
To transfer Google Calendar data, simply log in with the same Google account on your new device, and your calendar data will automatically sync. There is no need to perform a manual backup.
Thank you for your understanding.