Microsoft hasn’t shied away from talking about Arm with Windows 11. In addition to the new design, Office will also adapt to your Windows light / dark mode, so you should be able to avoid the experience of opening a document and having it blast light into your eyes at night. While it uses a similar design to Windows 11, it’ll be available whether you're running the Windows 11 Preview or Windows 10. Microsoft also announced a redesign of Office, which you can see above and below.
The new version of Office is currently in beta, available to Office Insiders. Microsoft is announcing that the next version of Office for Windows 11 will have a native 64-bit Arm version, for improved performance on large or picture-filled documents, and support for 64-bit add-ins.