This script can search calendar items in a shared mailbox in Office 365 Exchange Online. You need to add proper permission to a shared mailbox folder before running this script.
Currently, you can easily search calendar items in Outlook. But you find this feature is not available in Outlook Web App (OWA). You want to find a workaround for those people who use Outlook Web App only.
You can find more All-In-One Script Framework script samples at https://aka.ms/onescriptingallery