In Google Calendar, if your users have a work profile on their Android device, they may want to view their personal and work calendars together. To use this feature, your organization's Enterprise Mobility Management (EMM) must support the Android feature, and admins and users must enable the feature.
If you manage apps and devices with Google endpoint management, you can turn on this option for the Android Google Calendar app. For instructions, go to Manage mobile apps for your organization - Allow Android users to see personal data in a work app.