I was about to make a suggestion, but did some cursory research and then became confused probably similar to you. I was also reminded why not all Cloud syncing services are the same.
My experience with One Drive for example; one can micromanage what is on device, what is in the cloud and what is synced to both. Such as right clicking on any item selecting “Free up space” ceases to sync a copy of that item on the device.
I have not been able to find anything that suggests iCloud having any ability to micromanage what is synced on a device, it seems to be an ALL or “some” with one setting - Optimize iPhone Storage.
Tap Sync this iPhone. In iOS 15 or earlier, tap to turn on iCloud Photos.
Select Optimize iPhone Storage to save space on your device.
" When Optimize Storage is turned on, full-resolution photos and videos are stored in iCloud, and, when needed, space-saving copies are stored on your device. And as long as you have enough space in iCloud, you can store as many photos and videos as you want. "
So the moment iCloud Photos sync is enabled on the new iPhone its going to attempt to sync it ALL from my understanding.
I was about to make a suggestion, but did some cursory research and then became confused probably similar to you. I was also reminded why not all Cloud syncing services are the same.
My experience with One Drive for example; one can micromanage what is on device, what is in the cloud and what is synced to both. Such as right clicking on any item selecting “Free up space” ceases to sync a copy of that item on the device.
I have not been able to find anything that suggests iCloud having any ability to micromanage what is synced on a device, it seems to be an ALL or “some” with one setting - Optimize iPhone Storage.
https://support.apple.com/en-us/HT205703
Tap Settings > [your name] > iCloud > Photos.
Tap Sync this iPhone. In iOS 15 or earlier, tap to turn on iCloud Photos.
Select Optimize iPhone Storage to save space on your device.
" When Optimize Storage is turned on, full-resolution photos and videos are stored in iCloud, and, when needed, space-saving copies are stored on your device. And as long as you have enough space in iCloud, you can store as many photos and videos as you want. "
So the moment iCloud Photos sync is enabled on the new iPhone its going to attempt to sync it ALL from my understanding.