Certainly - WebAuthn is an open standard, and passkey appears to just be "passwordless FIDO2" (all open standards) with shiny branding around it.
That means anyone can implement it, including a physical token (which can be entirely open source, like the solokeys dongle).
The real concern here is friction for the "average end user" - passkeys IMHO are a net-good thing, as long as we don't see this result in everyone regressing towards "single factor auth" in some way. As it stands though, WebAuthn/Passkey gives you a level of phishing resistance that ought to raise the bar on compromising accounts.
The part I do fear about third party password managers is that they'll potentially end up lowering the level of security that WebAuthn heralded, by normalising pure "software" authenticators - putting TOTP seeds into bitwarden alongside passwords feels like putting all your eggs in one basket, even if it's a reasonably good basket. A physical WebAuthn key gives you a level of hardware isolation (limited attack surface, time-bounded attack surface, physical contact required per-authentication) that will be lost if everyone moves to software-based tokens.
On the other hand, if people are replacing a globally re-used password with a "passkey", it's a lot better. If they are replacing a hardware token with a software token, that's a small step backwards. If most people are still manually using the same password everywhere, it's probably a net step forwards.