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Those are the low resolution space-saving Optimized versions.
For information about Optimized photos, see the following from Set up and use iCloud Photos - Apple Support
If you turn on Optimize Storage, iCloud Photos automatically manages the size of your library on your device. Your original photos and videos are stored in iCloud and space-saving versions are kept on your device. Your library is optimized only when you need space, starting with the photos and videos you access least. You can download the original photos and videos over Wi-Fi or cellular when you need them.
If you turn on Download Originals, iCloud Photos keeps your original, full-resolution photos and videos in iCloud and on your device.
Before turning off iCloud Photos, open the Photos app on your Mac, click Preferences (or Settings) on the Photos menu, click iCloud at the top of the Preferences or Settings window, click "Download originals to this Mac" and allow time for the originals to be downloaded.
Also see the "How do I turn off iCloud Photos on only one device?" and the "How do I remove all iCloud Photos content from iCloud and my devices?" sections of Get help with iCloud Photos - Apple Support