It’s the way ‘subscription’ or annual fee Microsoft 365 works. Microsoft calls that ‘per user’ licencing. That’s enforced by the separate login within the Microsoft 365 programs. However, each person using Microsoft 365 needs to have a separate licence to use the software. Once Microsoft 365 is installed on a Windows or Mac computer, any login to that device can use the software. This is the crucial login for Microsoft 365 / Office 365 use.
Microsoft account login within Microsoft 365 programs (Word 365, Excel 365, PowerPoint 365, Outlook 365 etc) at top right on the title bar.
Login screens: Windows (left) and Mac (right)
Microsoft Office is licenced in two different ways: Once you’ve installed Office on a computer it’s available to all regular users on that machine however the licencing rules matter. Windows 10 for Microsoft Office users has a chapter devoted to multi-user setup and use including making a ‘Guest’ account (which Microsoft stopped providing but we show how to restore Guest to Windows 10). Most commonly, there are separate Windows or Mac logins for the computer with each user/login having their own folders for documents etc. Office can work for multiple separate users on the one computer. It depends on which type of Office you have on a Windows or Mac computer. Microsoft Office rules might let two users or more use the same copy of Office on a computer.