I recently ran into the problem: Cloud storage shows full - but no files to be found anywhere (LR-Classic, LR-Web, Adobe Creative Cloud, Adobe Acrobat etc.)
I made sure (after securing everything locally) that no file would be anywhere anymore. I basically deleted everything yet the cloud was still full. Checking in the community, I stumbled over "synchronisation errors". Nevertheless I could not find the corresponding section in the LR-Web among the "All Photos" entries. Here is how I found them after all:
1. Step: Condition: You also do not see the section "Synchronisation Error", when the arrow next to "All Photots" points downwards. If you see it you can manage the files there, if not proceed to step 2.
2. Step: If you dont find it, go to LR-Classic, "Preferences" --> "Lightroom Sync" and you will find the following overview for your "Sync Acitivities" and you might find entries with a link for each one. Select the link and you will be guided to the preview in LR-Web.
3. Step: In the preview you wont see much due to the synchronisation error, in order to jump to all synchronisation errors you have to click on the cross in the top-right-hand corner. Then you will jump to the overview in LR-Web.
4. From there you will be suddenly in the folder "synchronisation error" with all errornous files listed up and you can delete them there and finaly clear them from your "Deleted Files" too. This cleared the cloud storage for me in the end. I hope this helps if you stumble across the same issue.