When using Exchange Online, you can connect any user calendar to the Calendar web part to view and add events directly within your SharePoint site.

Calendar is currently available in two implementations:

1. App part - the original calendar. It is deprecated and not recommended for use, but still functional. We generally do not recommend using this web part. Can only be used on Classic pages.
2. Client-side web part - the new version that is installed as part of Ultimate Forms Extensions and can be used on Modern and Classic pages. This is the recommended version and you are advised to upgrade.

To be able to access Exchange calendars, a global administrator must first grant access.

• When you add/update an Exchange data source in a calendar profile, a pop-up window will appear requesting permissions. You have to grant the permission to be able to save the data source.
• When using the client-side web part, you must grant client-side API access to Microsoft Graph. Your version of Ultimate Forms Extensions must be 1.2.0.0 or higher. Once you install the app, a new API access request will be submitted. You can view your pending access requests under SharePoint Administration -> Advanced -> API access. Without granting this permission, client-side web part won't be able to access Exchange calendars.

NOTE: currently only user calendars are supported by Microsoft for API access. Group/shared calendars cannot be used.