Hello Rushikesh Socha, Good day!Thank you for posting to Microsoft Community. We are happy to help you. After thorough research, testing from my end and consulting, it’s been concluded that there is not any keyboard shortcut currently available for this.
Reference: Keyboard shortcuts for Outlook - Microsoft Support.
As we have dedicated support team for Outlook for Mac related issue. So, I'd recommend you please kindly contact to our dedicated Outlook app for Mac support team via Help menu > Contact Support within Outlook for report or to double check with them.
We apologize if we are not able to meet your requirements; however, thank you for bringing this to our attention, we will surely raise you concerns to our Product Team and hopefully this can be included in the future updates. In the meantime, I did find almost similar post in the official feedback forum Calendar zoom in/out · Community (microsoft.com), Unable to zoom in a new mail composer window · Community (microsoft.com) and the product team is aware about this requirement and will update the status via the post. You can upvote or add a comment to push via the entry, i create for you in the Feedback Portal Outlook zoom in / zoom out · Community (microsoft.com), I have asked my team to vote, and you can share your vote and comments there as well.Thank you for your cooperation and understanding.For other concerns, please do not hesitate to add you post in the Microsoft Community Team.Appreciate your patience and understanding and thank you for your time and cooperation.Sincerely,Eben Ezer Tres | Microsoft Community Moderator