These two things are mutually exclusive. They can store encrypted backups on a server somewhere, but unless they have the decryption keys from both parties (E2E) then no, it can't be stored in plain-text.
If you don't encrypt the backups, they are unencrypted, yes. That's why you should encrypt your backups. It's baked right into WhatsApp on the screen where you manage your backups.
These two things are mutually exclusive. They can store encrypted backups on a server somewhere, but unless they have the decryption keys from both parties (E2E) then no, it can't be stored in plain-text.
If you don't encrypt the backups, they are unencrypted, yes. That's why you should encrypt your backups. It's baked right into WhatsApp on the screen where you manage your backups.
Sure. Also if you take a screenshot of every message and publish it on the Internet, then your messages will be public.