iOS users, please read this info about iCloud backups

If you have enabled iCloud backup for app data, this will include your password-encrypted MetaMask vault. If your password isn’t strong enough, and someone phishes your iCloud credentials, this can mean stolen funds.

You can disable iCloud backups for MetaMask specifically by turning off the toggle here:
Settings > Profile > iCloud > Manage Storage > Backups.

If you want to avoid iCloud surprising you with unrequested backups in the future, you can turn off this feature at:
Settings > Apple ID/iCloud > iCloud > iCloud Backup