You can disable iCloud backups for MetaMask specifically by turning off the toggle here:
Settings > Profile > iCloud > Manage Storage > Backups.
— MetaMask 🦊💙 (@MetaMask) April 17, 2022
Who was attacked?
This is how it happened, Got a phone call from apple, literally from apple (on my caller Id) Called it back because I suspected fraud and it was an apple number. So I believed them
They asked for a code that was sent to my phone and 2 seconds later my entire MetaMask was wiped
— Domenic Iacovone (@revive_dom) April 14, 2022
3/ MetaMask actually saves your seed phrase file on your iCloud. The scammers requested a password reset for the victim's Apple ID. After receiving the 2FA code, they were able to take control over the Apple ID, and access iCloud which gave them access to the victim's MetaMask.
— Serpent (@Serpent) April 17, 2022