Microsoft:

The latest release of apps including Word, Excel, PowerPoint, Outlook, OneNote, and OneDrive can be installed on devices that are based on the Apple Silicon architecture. For the best experience, install the November 2020 release (build 16.43), or later. This release of Office includes the latest optimizations for macOS Big Sur, which is the first operating system to support Apple Silicon.

And:

As demonstrated at Apple’s Worldwide Developer Conference (WWDC) in June 2020, we’ve already started the process of moving Mac apps to universal binaries. In the future we will natively support both Apple Silicon and Intel chipsets within the same executable.

In a nutshell, the apps noted above will run in Rosetta 2 emulation or, as they get rebuilt for M1, as native apps. But the features won’t change. They’ll just speed up as they go native. At least, that’s the idea.