The newest version (as of two years? ago) is a download; although I don't use the newer MS
Office, I understand some payment schedules are like lease instead of actual buying a license.
See the monthly, annual, or one-time (versions) with different associated costs and features.
• Compare All Microsoft Office Products | Microsoft Office
https://products.office.com/en-us/compare-all-microsoft-office-products
From the Mac App Store; download and buy a limited license.
• Mac Archives - Microsoft 365 Blog
https://www.microsoft.com/en-us/microsoft-365/blog/tag/mac/
• Office 365 for Mac, Office for Mac - microsoft/us
https://products.office.com/en-us/mac/microsoft-office-for-mac
There must be a contact by phone, or email; for sales humans(?)
You'd probably have to try the 'click-on to Buy' in the web pages.