I cannot find all my iCloud photos
I have had iCloud for over 5 years but can only find photos from the past 3 years
MacBook Pro 13″, macOS 10.14
Did you delete any photos from the connected devices?
If yes, this would have also deleted the photos from iCloud.
iCloud Photos can't be used as a backup for photos, it is meant to sync the photos and changes to all connected devices.
Also check this article:
If you're missing photos or videos in the Photos app - Apple Support