Am I able to purchase more than 2tb of storage monthly?
I need to expand my iCloud storage, because mine is full.
Question marked as
There isn't a 4TB plan as such; you have to do it by having a subscription to Apple One and also subscribing to an individual iCloud+ plan.
Refer to this document about how to do this --> What happens to your iCloud storage when you sign up for Apple One - Apple Support
"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."