Family sharing.
Family sharing Apple One subscription. Can we exclude iCloud storage from sharing?
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You can't select individual items.
This may be relevant in your situation though:
What happens to your iCloud storage when you sign up for Apple One - Apple Support
If a family member subscribes to Apple One
If you belong to a Family Sharing group and a family
member subscribes to an Apple One Family or Premier plan, you can
choose to keep your current iCloud+ plan or use the shared iCloud
storage in Apple One.
If your family needs additional iCloud storage, the family member who purchased Apple One can buy more iCloud storage. With both Apple One and an iCloud+ plan, your family can share up to 4TB of total iCloud storage.