With Passkeys, your credentials will automatically sync between devices. So as long as you have some way to log in to your main account (Apple/Google/Microsoft, etc.), then you should be able to maintain access to all other accounts, even if you’re always moving between devices.
And there is a solution to the single point of failure problem as well, because there is a built-in flow where you can copy the credentials to other platforms, in case you lose access to your main account.