Microsoft 365 is available for use on a Chromebook, but only via the web applications. Below is a summary, but this Microsoft KB article has more detail.
You cannot install Windows or Mac desktop versions of Microsoft 365 or Office 2016 on a Chromebook, you must use the Microsoft 365 web apps instead
The Microsoft 365 web apps will allow a user to
Microsoft's KB Article - How to access Microsoft Office on a Chromebook contains more details on how to access Office apps on a Chromebook.