I want to save my photos on iCloud but not on my Mac how do I do this

iCloud Photos is a syncing service. Any photo you delete from a device where iCloud Photos is turned on will also be deleted from iCloud and from any other device connected to iCloud Photos. You can potentially reduce the storage space required on a device by turning on Optimize Storage. See: https://support.apple.com/en-us/HT204264

Apple does not currently offer cloud-only storage for photos. If that is what you want or need, you may want to explore 3rd party options such as Google Photos or Dropbox.

Note the following from My Photo Stream - Apple Support

Photos in My Photo Stream are saved on the iCloud server for 30 days. After that, the photos are removed from iCloud.

Also note that it appears to be a service that may not be continued. See the following from the same link:

If you recently created your Apple ID, My Photo Stream might not be available. If My Photo Stream isn't available, use iCloud Photos to keep your photos and videos in iCloud.

If you want them only on the cloud with nothing on your Mac, that is your only choice but I don't know that the other options are any easier. You can try them to see what you think.