Not at all? The password manager handles that automatically, have you never used a password manager before?
> Passkeys will automate and enforce the check
What happens to the passkey when the origin changes, is it automatically recognising it as the new domain without any manual input? Curious to see what magic is responsible for that
Yes: '...you double-check the domain.' That's manually checking for mistakes.
> What happens to the passkey when the origin changes,
The passkey won't work at all. You will just have to create a new one.
Yes, but that's only when the origin changed compared to when you added it to the password manager. Same thing for Passkeys, won't work if the origin is different, so you double-check that the domain in your browser address bar is the correct one.
Obviously normally you don't do anything except click on the account that shows up, since the domain matches.
You could claim that a phishing site could set up their own passkey registration system–but that still wouldn't give them access to the target's real account.
So exactly the same as password managers, there is no functional difference if you were using a password manager...