Create a new passkey on the device? Or on the new device? I don't see why this is a big issue. Sure, it's slightly inconvenient to go through the 'create passkey' flow on a new device, but as long as the account you are using (let's say, GitHub) supports storing multiple passkeys per account and managing them online, there's no reason you can't.
For every single one of your 100+ accounts? What if you forget an account when doing so, then it's lost forever? If one of the 100+ websites is momentarily down I simply have to keep the old passkey provider around until it comes back up and then remember to switch just that one later?
