Google has introduced a new feature called Restore Credentials which saves your app login info and restores it seamlessly on new devices.
it says it is encrypted but it is encrypred using keys that google has access to as they are unlocked with you logging in into google account.
First it uses lock screen password, so google do not have access to this password.
Even if your lock screen is unfortunately your Google password, I think proper authentication protocol do not send your password to Google to authenticate, but only the hash, which cannot be reverted to derive your password.
Obviously, the above is assuming that Google is not malicious. Otherwise it can just use play service, which is privileged and closed source, to get all your data. If your threat model including Google itself trying to steal your key, you will probably need to install a trusted rom or use iOS (however, apple and the rom developer can also steal your key).
assuming that Google is not malicious
Previously they would need to push malicious code to your device to steal your login data, that is a risk that someone would do reverse engineering on that and expose it, now they will have the data on their servers and they can abuse it any time they want, I doubt they will use it to login as you, but they will use it as metadata to connect all your accounts for marketing.
proper authentication protocol do not send your password to Google to authenticate
That is not true for 99% services including google. Google have a plain text password at the time you are logging in, they just store hashed+salted version in storage.
(Almost) No website (or app) is hashing the password before sending it to server, so if you hack the login screen you can dump RAW passwords anytime.
