Then I have a backup yubikey at home for services which allow to register two keys. For other's there's still good old password+some second factor.

Then I use the authenticator built into my phone. Or the authenticator built into my desktop. Or the authenticator built into my laptop. Or my other authenticator.

My phone was destroyed not too long ago. I had been using it for passkeys. Oh no, all those passkeys were gone. No problem, when I got my new phone I just used the authenticator on my keyring to get back into my accounts. If my keyring authenticator got lost I'd just buy a new authenticator eventually and add it to my accounts.

I open the safe where I keep my spare Yubikey. Or I use the passkey stored in my phone, or the one on my laptop. Make passkeys, put them everywhere.