Hi @Rising Flight,
Here are the steps about how to add Rhythm of Business Calendar for a SharePoint site.
1.Please follow this article to first go to the SharePoint store and request Rhythm of Business Calendar: Add an app to a site.
2.Please contact your tenant's administrator to agree to your request and add Rhythm of Business Calendar to your site: Manage app requests.
3.Now that Rhythm of Business Calendar has been added to your site. Rhythm of Business Calendar is similar to a web part, and you can add it to your site page just like you add a web part. If you do not know how to add a web part, please refer to this article: Using web parts on SharePoint pages.
Also, since Rhythm of Business Calendar is similar to a web part, its permissions are related to the page on which it is added. You can restrict access to Rhythm of Business Calendar by setting permissions for this page.
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