Windows 11 Home Product Key Confusion

What you bought is a digital licence (Microsoft calls it a digital entitlement). It's a record on Microsoft's activation servers that says, "this hardware is licensed for Windows 11 Home," optionally linked to your Microsoft account. There is no key.

You can't lose the key, because you can't lose what doesn't exist.

If you lose access to your Microsoft Account, your PC stays activated. The entitlement is bound primarily to a hash of your hardware, not to your account. Clean install the same edition, skip the key prompt, and it reactivates automatically over the internet without anyone signing in. The account link only matters in one scenario: you replace major hardware (motherboard, usually), the hash stops matching, and you need Settings, Activation, Troubleshoot, "I changed hardware on this device recently", that step needs the account. So it's worth keeping account recovery info current, have more than one MFA option, but a lockout doesn't cost you Windows.

On the ISO installer, click "I don't have a product key" and select the edition you bought.

For €145, you got a permanent, legitimate licence tied to your machine, transferable to a new PC later (retail terms, one active machine at a time). Same rights as a boxed copy, just no cardboard.