How can I use Microsoft 365 applications?
Only by using macOS 11, 10.15 or 10.14
*You can USE the Office suite if already installed, but the installer for new copies of the software require any of the three macOS version listed above.
Their support document here gives the details:
Office for Mac is supported on the three most recent versions of macOS. As new major versions of macOS are made generally available, Microsoft will drop support for the oldest version and support the newest and previous two versions of macOS. Product functionality and feature availability may vary on older systems. For the best experience, use the latest version of any operating system specified above.