Hello Allen,
Welcome to the Microsoft Community.
It seems you have some issue with the changes in Office themes. I understand that you have made some efforts to modify the default fonts. But I'm not sure if you have done the operations correctly. Editing a built-in theme across all Office applications can be a bit tricky, but here’s a step-by-step guide to help you change the default font from “Aptos” to “Calibri”:
- Open Word or Excel: These applications provide the most straightforward way to edit themes.
- Go to the Design Tab: In Word, click on the
Design tab; in Excel, it’s the Page Layout tab.
- Access the Fonts Menu: Click on
Fonts
and then choose Customize Fonts.
- Change the Body Font: In the
Create New Theme Fonts dialog, select “Calibri” as the body font.
- Change the Heading Font: Similarly, choose “Calibri” or another preferred font for headings.
- Save the Theme: Give your new theme a name and save it.
- Set as Default: To make this theme the default for all new documents, click on
Set as Default.

For Excel, if you’re unable to change the font directly, try setting the default font through the Excel Options:
- Open Excel Options: Go to
File > Options.
- Go to General Settings: In the Excel Options dialog, look for the
General settings.
- Change the Default Font: Here, you should be able to set “Calibri” as the default font.
Remember, these changes will apply to new documents or sheets you create. For existing documents, you’ll need to apply the newly created theme manually.
Change a theme and make it the default in Word or Excel - Microsoft Support
If you have any more questions or need further assistance, feel free to ask.
Best Regards,
William.Y | Microsoft Community Support Specialist