Change font in Immersive Reader for Office for the web and OneNote

Sign into your account at Microsoft365.com, select Word, or OneNote. Open your document, or a notebook page and select View > Immersive Reader 

• For Outlook for the web, log in at Office.com, select Mail, and open an email. Select More Options  , then Show in Immersive Reader.

Select the Text Preferences icon  to open Text Options.

Select one of the two options under Font.