Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Microsoft terminology is sometimes confusing. Specifically, product names are not always consistent.
If you have a subscription (= Microsoft 365), you should be able to install the most recent update, assuming that your version of macOS allows it.
If you have Office 2021, which is a perpetual license, you can install updates for as long as the product is supported.
See also https://www.brandwares.com/bestpractices/2023/03/most-recent-office-you-can-run-best-practices/ .
Note that you can't move from one perpetual license to another one without paying for it. In other words, you can't move from Office 2021 to Office 2024.