iCloud & iCloud Photos · iCloud Photos and the Photos library
Is iCloud Photos a backup of my photos?
Short answer: Not on its own — iCloud Photos syncs one library, so deletions and edits spread to every device. Keep a separate copy with Time Machine or exported originals; with Optimize Mac Storage on, download originals first.
Not on its own. iCloud Photos keeps one library in sync across your devices, so a photo deleted or edited on one device is deleted or changed everywhere. Recently Deleted gives you a short window to undo, but it isn't a separate history.
For a real backup, keep a copy somewhere else: back up the Mac's Photos library with Time Machine, or export originals to an external drive. With Optimize Mac Storage on, some originals live only in iCloud, so switch to Download Originals first if you want a complete local backup. See is iCloud Drive a backup.