How to disable kerning for first line in Outlook on iMac running Sonoma?

I have an iMac running Sonoma. Somehow I set my font to use kerning, but I can't remember how I did this (sigh). When I start a new message in Outlook, the first line uses kerning and a different font than the one I've set as the default for new messages. It only happens for the first line; successive lines use my default fault.

I'm using Legacy Outlook for macOS, and I've set my default fonts to Arial. I'm attaching an example and would appreciate your help! Thanks!

[Re-Titled by Moderator]