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?
Are you using every single one of the 100+ accounts constantly? No? Then you can do the passkey flow on demand as needed. It can be comparably simple as an email login or 'we emailed you an OTP' login confirmation flow. If you never get around to using the account ever again in your life, I suppose you never needed it?
If the website is momentarily down how are you going to access it with a password at that moment? You'd have to wait until it came back up. And then you could just as well set up the passkey.
I'm referring to the process of switching where my passkeys are stored to a different place. E.g. moving from them being stored by Apple to them being stored by Google or any other provider.
