From what we can gather, one cannot select what iCloud backs up until a backup is created. That’s nuts to me but that’s the ways it appears to work. This is what one of our higher level colleagues had to say about this.
Seems like the backup process needs to first take an assessment of the device and what is on it initially by backing it up first. Then it will have the required info from that backup to allow the user-selection process of the items.
The only solution that I can suggest is to buy more storage, then backup, remove photos from the backup and then downgrade the storage plan. iCloud+ Storage plans start at 99¢ USD for a 50GB plan.
Should you care to try this, read this.
Upgrade to iCloud+ - Apple Support
If you do decide to try that and you want to downgrade, see this.
Downgrade or cancel your iCloud+ plan - Apple Support
I realize that this isn’t ideal and frankly, I think it’s dumb that one would have to jump through hoops like this to pick and choose what to backup, but Apple in its divine wisdom doesn’t seem to give us any other way to do this.
It wouldn’t be quite so bad if Apple gave users 10GB of storage out of the gate where a lot of light users would have the space to back up and then pick and choose from there. But 5GB of storage is chump change in the overall scheme of things.
I wish I had something more for you, but at this point, that’s the only thing I (we) can think of.
