It's not recommended to sideload the Office apps, as the Web version works just as well. You can disable this mode after the app is installed. However, sideloading means enabling Developer Mode, which invalidates your warranty and removes all data from your device.
If you didn't already have the app, you can sideload it using an APK file of the Microsoft Office Android app. However, if you've already downloaded the app or sideload it now, you're still free to use it, but there won't be any more updates. Microsoft ended support for this method as of September 18, 2021.
