The deleted files can be found see this article https://support.apple.com/en-in/HT203052
Where to find missing files
When you turn on iCloud Drive, any documents that you already store in iCloud automatically move to iCloud Drive. You can see your files on iCloud.com, in the Files app on iOS 11 and later, in the Pages, Numbers, and Keynote apps, or in the iCloud Drive app on iOS 10 and iOS 9.
If you don’t see your files in any of those locations, set up iCloud Drive on all of your devices.
If you need to access a file that you deleted within the last 30 days, you can get it back from the Recently Deleted folder in the Files app, or on iCloud.com.
Not only files store the iCloud space , the other applications like photos , notes ...also consume the space see the brief details in this article https://support.apple.com/kb/ph2608?locale=en_US
You can reduce the space see this article https://support.apple.com/en-in/HT204247