Using Classic Outlook on Windows for personal email, calendar, and contact management
So apparently there is a way to change the "zoom" level in the reading pane - parentally.
See this video https://www.youtube.com/watch?v=9yfyy5Xfl4k&t=2s
All you have to do is while you are looking at an email in reading pane - increase the zoom level from bottom right section, adjust to the percentage of your liking, and then double click the percentage - a small window will pop - in that click / check "remember my preference" and all your emails will appear with that level of magnification in your reading pane.
Hope this helps.
Thank you,
Mehul