Troubleshooting ways if default font changes does not apply correctly:

- Ensure the email format is set to HTML or Rich Text
- Restart Outlook to apply changes
- Verify Stationery Settings
- Ensure outlook is up to date.
- Check Policies if you are working in an organization
- Create a New Profile if the current one is corrupted.
- Disable Add-ins that might interfere.
- Test on Another Device.
- Reinstall Outlook
Learn how to change default font in outlook effectively by reading the blog.