Storing Phtos in icloud

I do not have a storage problem as I have 1.7TB of 2TB available on my iCloud account. I recently downloaded more than 3000 photos to the Photo app on my Macbook Air. Only 600 of those photos are available in my icloud photos. How do I get the remaining 2400 odd into iCloud? (I think I've nominated an older Macbook Air. The one that has the photos has OS 12.7.2)