Noted that files were missing after the installation of iCloud, pay attention to sync your important files from Google Drive to iCloud Drive.
1. To recover lost files in the iCloud Drive App Folder, please go check Recently Deleted.
2. Before proceeding with data recovery software, it's advisable to consult with Apple Support or a technical expert familiar with iCloud Drive.
3. Use iBoysoft Data Recovery for Mac to retrieve your lost files. It's easy to use and user-friendly, please follow the instructions provided by the software.
Best Deleted File Recovery Software - iBoysoft Data Recovery for Mac
You can also refer to How To Restore Deleted Files From iCloud Drive On Mac/MacBook Air/Pro?