Passkeys and OIDC are not directly related. If all you want is "authenticate to AWS" then yes, passkeys would work, but so would a simple password, or a TLS client certificate, or whatever other technology you like for authentication.

OIDC works for things like "use my employer's login to get access to AWS resources without having a separate AWS password".

For certain OIDC authentication implementations, you can actually use passkeys. Standard passkeys should work perfectly fine with Keycloak's WebAuthn implementation, for example, either as a second factor or as the first factor in the login flow.

Personally, I would be worried about losing access to an account if I only relied on a passkey.

How can I backup a passkey on a sheet of paper?