I had iCloud set up and working and it does work with photos taken from the camera (only). However, many iPad apps have an option to upload via "iCloud Photo Sharing" that seems to have nothing to do with the Photo Library in iCloud despite sharing with same logo.
For example, I created a so-called shared album with "iCloud Photo Sharing" on iPad and my iCloud does not show any change; similarly when I created a different album in Photo Library on iCloud, the "iCloud Photo Sharing" on my iPad cannot see it.
I was using the Vectornator app and could not save work (svg) to iCloud. This should be very simple but unfortunately is very confusing for a first time iPad user. How do I work with photos/images basic cloud-uploading not from camera but from app?