> At minimum, a credential manager distributed for wide use should encrypt exported/copied keys with a user selected secret or user generated key.

It feels like this stated minimum is not your actual minimum.

Consider for example a macOS user keychain. The keychain is encrypted on disk with a user-selected password. But once you unlock the keychain with the password, you can copy and paste passwords in clear text. The keychain is not a black hole where nothing ever escapes. And I have no objection to this setup; in fact it's my current setup.

So when you say copy and paste of passkeys in clear text is not a good idea, there's nothing inherent to encrypting credentials with a user key that prevents such copy and paste. There would have to be some additional restriction.