[Mobile] Storage Full Notification

Have you created and deleted a lot of projects? Do you have a Creative Cloud subscription or just Adobe Express? There are different storage quotas for different plans. https://helpx.adobe.com/uk/creative-cloud/kb/file-storage-quota.html

Check all these locations for any files that count towards your storage limit:
https://assets.adobe.com
- check also the deleted files section - files are permanently deleted after 30 days but until then do count towards your storage limits;
https://lightroom.adobe.com
https://documentcloud.adobe.com
https://express.adobe.com/sp/
https://new.express.adobe.com/
https://assets.adobe.com/mobilecreations
- in the Mobile Creations area also check Deleted items.

Here's the help article about cloud storage and what is included as you may use other parts of it e.g. Libraries or Lightroom, that you haven't mentioned here:
https://helpx.adobe.com/creative-cloud/kb/file-storage-quota.html