Does Apple make backups of iCloud? Photos have been deleted from an iPhone which had iCloud Photo Library turned on so photos were deleted from iCloud as well. Does Apple store backups of iCloud to restore its state at a previous date ?
Does Apple make backups of iCloud?

From an infrastructure management perspective, yes they do. However, it’s not something consumers can access alone and it’s not something Apple support staff and engineers can access alone. Their backups are for service continuity; if something on their servers crash, they can be to and running again. They also have some automation in case people inadvertently make a choice to delete files not realizing that deletion is permanent. Due to how the encryption keys are stored, you would need to create a support pin and then explicitly give Apple consent and a key to unlock your files. Think of a bank offering to store your lock box in their vault. They can look at your box, but may not have the key to open it.
Can you access this back up?  No. It’s not for users. In fact, every Apple account is encrypted meaning Apple can’t make sense of the files without your help.
From the customer perspective (yours) iCloud is a synchronization service. If you delete photos, it’s assumed you wanted them gone. Now, you can use iCloud for your own backups, but that’s something you have to setup and manage (For example, my iPhone is backed up to iCloud including photos on it).
IMO, iCloud is good, but not as mature as OneDrive or Azure. In those services, not only do I get the synchronization services like iCloud, but I can purchase a backup plan and even specify where I want it (I could be in the east coast of the US and my data gets backed up to the west coast or even Europe!)
Personally, when it comes to Photos, I have them in the cloud, on my NAS and then backed up from the NAS to a USB drive, so 3 places. Having your own backup is the ideal case as you would not depend on support for recovering files you could have backed up.