It is a subscription, it is not permanent.
Click on the link to read about "Downgrade or cancel your iCloud storage plan" on an iOS device, a Mac, or a PC. --> https://support.apple.com/HT207594
"What happens when you decrease your storage plan
When you downgrade your iCloud storage plan, the storage decrease takes effect after your current monthly or annual subscription ends.
If you downgrade or cancel your plan and your stored iCloud content exceeds your available storage, new photos and videos don’t upload to iCloud Photos, files don't upload in iCloud Drive, Messages in iCloud don't update, and your iOS devices don't back up. Learn how to manage your storage by deleting the information that you don't need anymore.
If you downgrade to the free iCloud Storage plan, you'll have 5GB of storage."
March 2021 post by ASC contributor Michael Black
https://discussions.apple.com/thread/252568292?answerId=254839872022#254839872022
- "When people cancel a subscription, they get an email saying they have 30 days to transfer their data for safe keeping, after which data will be purged to fit within 5GB."
