Looks good, but seems like its only for the computer not for pics saved to cloud
You won't find a service (certainly not a free, which is likely what you are looking for) that downloads all your photos (which is what they need to do to compare for dupes) from all clouds and then takes care of them in the cloud, and also works on local hard drive. It's an unreasonable ask.
You really should get around to download them all to a hard drive (anyway, can't be bad to also keep a local copy), filter and delete the dupes locally, and then clear and re-upload to the clouds what you want.