problem to downgrade back to 5GB (free) plan even storage size is below 5GB

Hey utshoward,

It looks like you're coming from the article: Downgrade or cancel your iCloud+ plan - Apple Support

"Before you downgrade or cancel your iCloud+ plan, first download or remove content that exceeds your new storage amount. To make sure that you don't lose any information, learn how to copy what you store in iCloud."

That would have the best information for you on downgrading your plan. You may need to remove other content such as iCloud backups to free up enough space. You can find more information on managing iCloud Storage here: Manage your iCloud storage - Apple Support

"Make more space available in iCloud

If you run out of iCloud storage, your device won’t back up to iCloud, new photos and videos won't upload to iCloud Photos, and iCloud Drive, other iCloud apps, and messages won't stay up to date across your devices. And you also won't be able to send or receive emails with your iCloud email address.

You can free up storage in iCloud by deleting content that you're not using:

1. Reduce the size of your iCloud Backup
2. Delete photos in iCloud Photos
3. Delete folders or files in iCloud Drive
4. Delete texts and attachments in Messages
5. Delete messages and manage Mail
6. Delete voice memos

Before you delete anything, you might want to archive or make copies of the information that you store in iCloud."

Thanks!