My MacBook has limited storage so I cannot do updates. It is filled with low resolution photos as I have optimized. If I delete the low resolution photos from my MacBook, will the high resolution counterparts remain on iCloud?
No.
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, but it sounds like you've already done that. See the following Apple article for more information: Set up and use iCloud Photos - Apple Support
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.
No.
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, but it sounds like you've already done that. See the following Apple article for more information: Set up and use iCloud Photos - Apple Support
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.
Can I delete photos from my MacBook and have them remain on iCloud?
