Microsoft Office no longer works. The window says sign in or purchase.

office 365 is subscription based. office 2016 for Mac is one time purchase.

office mostly does not come free, not even on computers shipped with windows.

Judithfelch wrote:

I purchased a MacBook Pro 2021 last year and purchased Microsoft Office also. Now Office...specifically Word does not work for new or old documents. A window comes up to buy or sign in to Word. Did I not realize that what I purchased was not forever like the Word on my old apple??

?

I have no idea about your third party subscription or your "forever like the Word "

did you sign in?

do you have to deactivate the old mac?

To activate a Microsoft Office 365 subscription you simply enter the email address you used when you extended the subscription with Microsoft.

if no insight for your third party app or can not sign in, or at a loss as to how to proceed to resolve your issue....

If in doubt refer to the developers website; Support/Help/FAQ/known issues/compatibility:

Microsoft Corporation/Customer service

1 (800) 642-7676

https://support.microsoft.com

Contact a third party vendor

Contact a third-party vendor - Apple Support

Ask the Microsoft Community

https://answers.microsoft.com/

Microsoft has now bumped the minimum supported operating system from Catalina to Big Sur for new installations of Microsoft 365 and most likely the only two supported single-purchase options: Office 2019/2021 for Mac.

Microsoft has their own unique definition of "forever". Your older Mac with its older operating system will continue to work with commensurately older versions of Microsoft documents... "forever".

It's up to you if you want to keep playing that game, but there are a number of excellent alternatives to Microsoft's bloatware. Life is better without it.