Getting iCloud Photos onto my iPad

So I have moved my whole Photo library from my iMac onto my 200GB iCloud Drive and can see it is being stored there and is accessible from my iMac. (I can now delete it from my C Drive.)

However my iPad and iPhone don’t seem to see the iCloud storage being used and can only access recent photos and some shared albums. How do I get the whole Library visible / sync’ed on my iOS iPhone and iPad devices? All my OS are up to date.

I have iCloud / Photos sharing turned on.