What happens to my data if I cancel my iCloud plan while my data is more than 5GB?

iCloud will no longer work properly and sync your data, if you are using more storage than you have subscribed for. Do not risk this. Download your documents and data and free storage, before you cancel your storage plan:

See: Downgrade or cancel your iCloud storage plan - Apple Support

"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 text messages won't stay up to date across your devices. And you can't send or receive emails with your iCloud email address.

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

• Manage your iCloud Backup
• Reduce the size of your iCloud Photos
• Delete folders or files in iCloud Drive
• Delete texts and attachments in Messages
• Delete messages and manage Mail
• Delete voice memos

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

You are very welcome 😊