Great in theory, but in practice there are still a frustrating amount of websites and services that put a low upper limit (usually just one or two) of the number of keys you can enroll.
This effectively makes it impossible to do what you’re saying. It sucks.
I hear this a lot but it hasn't generally been my experience. The only site I've personally come across that supports webauthn/passkeys but doesn't support multiple is the AWS management page. Which I essentially bypass by just configuring SSO and using an IdP which does support it.
Every other site I've come across that supports these things supports multiple. What common sites support only one or two?
This effectively makes it impossible to do what you’re saying. It sucks.