Passkeys get synced between your devices so they aren't any more fragile than passwords in a password manager.
Ideally this should have been hashed out before deploying passkeys everywhere, but I guess you can always register multiple passkeys for the sites that allow you to.
In a few years someone will post "how about a long human retainable passphrase?" as a new and improved discovery.
https://www.rfc-editor.org/rfc/rfc9807.html
https://en.wikipedia.org/wiki/Password-authenticated_key_agr...