What happens to my passkeys if I lose my device?
Your passkeys might be stored on your device, but they will also be made available to your other devices by the same vendor. If you have an iPhone, your passkeys will be available on your other apple products like a MacBook or iPad. If you have an Android phone, then it should be available in Chrome browsers or an Android tablet.
You can choose to use a password manager (known as a credential manager) by a company who don't make your device. If you do, your passkeys will be available anywhere you are logged into it.
If you only have one device, then you just need to get back into the main account (Apple iCloud, Google Account, or the credential manager) and you'll have all your passkeys back.