Microsoft Office 2019 not working after Monterey Upgrade

If you downloaded Microsoft Office applications from the Mac App Store, they are strictly subscription versions. I only have Office 2021 for Mac installed (cost $40), so cannot speak to whether Office 2019 for Mac can get further updates now. It won't be retired for another year and as it is 64-bit application suite, it should work on Monterey — though not expressly designed for this operating system.

Do you need MS Office for corporate or customer document collaboration, or just need a competent suite that can open and create Office documents without dealing with Microsoft? Softmaker has an Office 2021 Mac, that has an MS Office visual metaphor, and can directly open Office documents. It has a trial and a non-punishing price. Available for Mac, Linux, iOS, Windoze, and Android. Maybe this is all you need.

You have replaced your Office 2019 single-purchase applications with the subscription-only Microsoft 365 applications from the Mac App Store, and without a subscription to Microsoft 365, those v16.64 applications will not work. You will need to remove those Microsoft 365 subscription applications, and reinstall Office 2019 for Mac so you have the correct applications for your single-purchase license. This all assumes that the Microsoft 365 applications when installed did not write data somewhere on your Mac that a casual application removal does not catch, and cause problems after reinstallation.

If you had installed that single-purchase of Office 2019 for Mac on another Mac, then your license is tied to that hardware, and a new installation on a different Mac would require either another license purchase, or contacting Microsoft to see if they will transfer the license to your existing Mac.

If you're not bound to using MS Office there are two, free, open-source alternatives, LibreOffice and SoftMaker FreeOffice 2018, that work pretty good, particularly LibreOffice. Both can open, edit and save MS Office documents in MS Office formats or in their own format.