Turn sound effects off in Outlook

New message notifications

1. Click the File tab.

2. Click Options > Mail.

3. Under Message Arrival, select or clear the Play a sound check box.

Link: https://support.microsoft.com/en-us/office/turn-sound-effects-on-or-off-in-outlook-e37d6cb4-5313-4d60-87fd-c4a7c2e4df59