A family of Microsoft word processing software products for creating web, email, and print documents.
Sorry, Big Sur no longer supports Microsoft 365 desktop programs. As alternatives, you can use Word for the web or Google Docs. For desktop software, take a look at open-source LibreOffice, which has good compatibility with Office file formats.
If you're adventurous, Open Core Legacy Patcher allows you to run newer versions of macOS on older Macs. You can install up to Sequoia (Tahoe is not supported). I have a 2011 MacBook Pro running Sequoia and the current edition of Office.