Android doesn't encrypt everything, and the details of what it does and doesn't encrypt are so fiddly that I don't feel confident enough to enable cloud backups.

Android encrypts its whole backup with E2E encryption using your PIN.

It doesn't, it encrypt some of your backup, and isn't entirely clear on which part.

No, iOS backups are not e2ee unless you go and opt-in to it, which approximately 0% have done.

Not in the UK for icloud