People wrongly think passkeys are like Bitcoin wallets, where losing them means there's absolutely nothing you can do, your account is simply lost forever.
Losing a passkey is exactly like losing your password, which is to say, that for 99% of services, you can reset your password/passkey really easily. There's a prominent "Reset Password" button right on the login form. It sends you an email or an SMS, you click it, and it lets you reset right then and there. You can reset your passkey in exactly the same way.
It is not that easy to reset if you lose your password to your Apple, Google, Facebook, etc. They all have a bunch of factors that they use to authenticate you if you reset your password, and they don't even document which ones they use.
So, if you care about those accounts, you've got to make sure you have backup access. They all let you generate and print "backup codes" (emergency passwords) and store them in a fireproof safe or a literal bank vault. Do that!
As everybody knows, you can't store all of your passwords in a password manager. You need something outside of the password manager to login to the manager itself. That's why 1Password/LastPass is called that; you still need one last password that you keep and manage yourself.
That's true of passkeys, too. You can login to Google with passkey, but if Google is your password manager that stores your passkey, you need something else outside of Google's password manager to login to Google. Whether it's a password, a backup code, a YubiKey, whatever, you need one more thing to login to Google, ideally more than one, so you can back it up and keep it safe.