Can iCloud sync be disabled

You can turn iCloud Sync on or off for each data type, but if you turn it off you would be well advised to do regular backups of your iPhone, because without sync if the phone is damaged, lost or stolen all of your notes, photos and everything else you have on the phone will be gone forever.

iCloud+ has 2 independent functions. iCloud backups, and iCloud sync. It’s confusing because they both have the same name prefix. But they have no connection with each other. Go to Settings/[your name]/iCloud. You will see a bunch of switches (with iOS 16 or later also tap Show All). When you turn on a switch that data type will sync to iCloud. If you do this on multiple devices that share an Apple ID the selected data will sync to all of those devices. 

You can also turn on iCloud Backups. This will back up your phone every night if the phone is plugged in, connected to Wi-Fi and locked.

But note that these are independent functions; anything that you sync by the first method will be excluded from the iCloud backups.

You get other benefits with iCloud+

• Hide my Email, which lets you access websites without giving away your primary email account (and also track who they sell your identity to)
• Private Relay, which is sort of a super VPN (at much lower cost than commercial VPN)
• Custom email domain, so you can create a personalized email address that forwards to your Apple ID email (such as jane@doe.com)

iCloud Photos and iCloud Notes are supposed to sync every time there is a change (e.g., new photo, deleted photo, edited photo) and there is supposed to be the same photos and notes on every device where those are turned on.

Also, iCloud Photos is a syncing service. Any photo you delete from a device where iCloud Photos is turned on will also be deleted from iCloud and from any other device connected to iCloud Photos. You can potentially reduce the storage space required on a device by turning on Optimize Storage. See the following Apple article for more information: Set up and use iCloud Photos - Apple Support

iCloud synchronization is supposed to cause the data to appear both in iCloud, and in all devices synchronized to it. Each device compares what it has against what is in iCloud – uploading its own updates, and downloading updates left in iCloud by other devices.

In this fashion, two or more devices that synchronize with iCloud can indirectly synchronize with each other.

Even if your iPhone is the only device connected to iCloud, there are benefits to iCloud synchronization. Should the iPhone get run over by a truck,

• Synchronizing a new iPhone to iCloud would get any data that had made it to iCloud back
• Even before you got the new iPhone, you could log into iCloud on the Web ( https://www.icloud.com/ ) and look at your data

Lawrence Finch wrote:

iCloud+ has 2 independent functions. iCloud backups, and iCloud sync. It’s confusing because they both have the same name prefix. But they have no connection with each other.

There is one connection, which you noted later on:

anything that you sync by the first method will be excluded from the iCloud backups.

This prevents redundant storage of the same data, and Is a tacit admission that iCloud synchronization can act as a kind of backup.

You have three options for backing up photos using iCloud:

• Use iCloud Photos
• Instead of using iCloud Photos, make iCloud backups and make sure your settings say to include photos in those backups
• Fail to back up your photos either using iCloud Photos or using iCloud backups. Unless you are backing up your photos outside of iCloud, this is a recipe for losing them

Between the first and second choices, iCloud Photos is much better. Either way, photos will take space in iCloud – but if you are using iCloud Photos, they will synchronize to other devices and be visible through the Web interface; and your backups will presumably complete more quickly. A complete win all of the way around.