[_trampeltier]

The same for me. I bought 2 keys and the idea was to have one as a backup key. But I did not find a way to do it. Anyway, even after read about how it works on some websites and watched some videos, the whole things is still a bit of a black box for me. I have no idea how a non-techie at moment a such device can use safe.

[sammorrowdrums]

I just bought two keys and most services let me enroll two devices or can use Yubico Authenticator, so I scan the OTP barcode twice, and tap each key one time on phone.

Then I'm going to sit with my wife and do that for some of her accounts and she will hold my backup.

edit for clarification, you really do need to have two devices with you to safely enough register 2fa, but obiously it is not safe to keep them both with you after initial setup, in case you lose them both. For the most part you just switch it on for everything with dual keys somehow (even if one registered key plus one Yubi Authenticator OTP).

For services that only actually enable one key, if they have emergency backup codes keep them in password manager, physical safe or a somewhere in your home depending on your threat level and the risks of the particular service being compromised.