A lot of companies still mess up passkeys, Allowing them only as a 1:1, using one terminates the session of another, or in some cases invalidates the previous passkey entirely.
Its implementations specific I'm sure, hwoever its not as straight forward as one would hope.
Also a favorite: "Your browser does not support Passkeys".
It sure does, which these horrible sites could easily verify by invoking the single line of JavaScript [1] to learn as much, instead of assuming "Firefox -> must be unsupported". Absolutely infuriating.
Its implementations specific I'm sure, hwoever its not as straight forward as one would hope.