Hi,To sync Odoo Calendar with your Outlook calendar, follow these steps:

1. Register the Application from in Microsoft Azure account.

2. After that, you will see a Client ID generated, and to generate a Client secret key, you need to click Add a certificate or secret. Certificates are optional.

3. Configure the Outlook calendar in Odoo using these credentials.Go to Settings, General Settings, and activate Outlook Calendar.

4. Go to the Calendar App and click the Outlook sync button.

5. After clicking the Outlook sync button, you are asked to log in to your account.

For more reference check this blog How to Sync Microsoft Calendar With Odoo

Hope it helps