It was my understanding that the backups are unencrypted. Is that still the case?
Exactly who has the ability to decrypt the backup is not totally clear.
It may be a different situation for non-Android users, Android users who are not signed in with a Google account, Android users who are not using Google Play Services, etc.
I remember that you had to extract at least two keys from the android device to be able to read "on-device" chat storage in the days of yore, so the tech is there.
If you don't have the keys' copies in the Google Drive side, we can say that they are at least "superficially" encrypted.