Hi Robin bro,
I have done factory reset after i backup my whats app, now when i tried to restore the whats app back up not available. But my i cloud showing 2.3 GB
After restore when we try to setup whatsapp first time, it shows restore option bro. If there is no old data in whatsapp you can try reinstalling whatsapp once again and let it check from iCloud Restore option.
Otherwise Try app offload method and check again bro.
Also We should take backup of whatsapp before doing Factory Reset bro. If you have done factory reset and then took backup of whatsapp as mentioned, its not possible to get the data.
2.3 GB file size could be older backup or other data. Try the steps I have suggested and see.