Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Depending on how you upgraded your computer to Windows 11, you may have lost the preinstalled version of Office 2019. Note that a product name which includes Office indicates a perpetual license, not a subscription.
If Office 2019 was previously associated with an account of yours at https://account.microsoft.com/services, you should be able to reinstall it from there.
The Microsoft 365 (Office) app does not give you access to a full subscription version, only to the Office dashboard.