Need more storage on my Mac Desktop

If you have already set up iCloud photo library in Mac see this article https://support.apple.com/en-in/HT204264

And you delete massive quantity of photos see this article https://support.apple.com/en-in/guide/photos/delete-photos-or-recover-deleted-ones-pht3bfab2f96/4.0/mac/10.14

Tip: If you’re deleting photos to free up storage space, remember that you must also delete them from the Recently Deleted album to remove them from your computer.

Read this also https://support.apple.com/en-in/guide/photos/from-icloud-photos-phtf5e48489c/4.0/mac/10.14

To delete an item from iCloud Photos, just delete it from your Photos library. 

• In the Photos app  on your Mac, select the items you want to delete, then press Delete.

Deleted photos and videos aren’t immediately removed from your library; they’re placed in the Recently Deleted album, where they remain for the number of days shown, and then are deleted. To remove the items immediately so that they’re no longer available on any device that uses iCloud Photos .

Yes you can access the photos in www.icloud.com by entering the Apple ID and password in recently deleted folder , make sure view them before 30 days , after 30 days photos are deleted from iCloud server .

jrjrod02 wrote:

What about if I buy another computer, how I do restore my photos from the icloud?

First of all, iCloud is not a backup for photos, or any data for that matter.

So are you saying that you will have two computers?

If you have iCloud Photo Library enabled on any device, the photo collection will be identical on all the devices which are signed into iCloud Photos with the same Apple ID. Deletion of a photo from any device will delete that photo from all devices which are using the same Apple ID for iCloud Photo Library.

Archive or make copies of the information you store in iCloud - Apple Support lists the proper way to archive photos.

What do you want to achieve?

Do you want to transfer your photos from an old computer to a new computer?

And then delete the photos from the old computer?

As Ferd II explained, iCloud will sync the deletion across all devices to keep the photo libraries identical. If you want to keep photos in iCloud Photos, but want to deleted them from one of your devices, you have to disable iCloud Photos on that device after syncing the photos to iCloud. Only, if the device is no longer syncing with iCloud Photos, delete the photos from the device. But then you can no longer use the Photos.app to access the photos in iCloud on the computer where you disabled iCloud Photos.

No.