Atlassian Cloud storage policy
What is Atlassian Cloud storage policy?
Please review the Atlassian Cloud Storage Policy documentation for details.
Extend Confluence Cloud storage with a plugin + 3rd party service:
Add-ons like the Filestack for Confluence, Office Files & Documents for Confluence, or Simple Cloud Files will also allow you to connect files from your cloud file services to your Confluence pages. Because these files are not actually hosted in Atlassian Cloud, they would not count toward your storage limit allowing you to extend the allotted storage amount as described by Atlassian Cloud storage policy.