Questions about passkeys

I am confused too. No doubt these queries have been answered elsewhere. Sorry.
How do passkeys work on a multi-user PC? In practice, does 1Password itself become a device? So that the passkey is stored on 1Password.
But if this is so, how is that different from a password? (Apart from length of course.)
And how is storing a passkey in 1Password device-specific? Would it not be "1Password-account-specific"?
If so, is the Windows Security instruction that says, "Choose a device with a saved passkey" strictly incorrect?
If I'm on track with the above, do passkeys not simply move the "weakest link"
FROM EITHER (a) the strength of the password (on the “app” you’re trying to log in to),
TO the strength of security on the “1Password account” (which happens to be, incidentally, on a device)?
(Both of these require device-security on the device also.)
-Gardenopolous