Because they force you to use online accounts now, you can get it from the registered account via the Microsoft account page.
In your Microsoft account: Open a web browser on another device. Go to https://account.microsoft.com/devices/recoverykey to find your recovery key.
I feel like you had to learn how to use it, operators and phrasing etc. They dumbed it down with search suggestions and even further by changing search terms to synonyms, and now outright ignoring terms. Height of Internet search was definitely pre 2008. More like 2005.