I think Microsoft sells both one-time-payment versions of Office, and subscription versions of Office (now renamed to Microsoft 365). But they will probably push you towards the subscription.
https://www.microsoft.com/en-us/microsoft-365?rtc=1
https://www.microsoft.com/en-us/microsoft-365/buy/compare-all-microsoft-365-products?tab=1
Here we go ... you can get Office Home & Student 2021 (one-time purchase) for $150, to run on a single PC or Mac, versus Microsoft 365 Personal, which is tied to one person (not one device) and costs $70/year. With Office Home & Student, you don't get Outlook (Microsoft's e-mail application) or some other things (see their chart).
There is a Free and Open Source office suite called LibreOffice that can open many Microsoft Office documents. It has versions for macOS, Windows, and Linux.
https://www.libreoffice.org/