Private and shared albums iPad Pro 3rd generation

Which system version is installed on your iPad? And what exactly is not working as expected?

Have you tried to add the photos from the album to the Shared album this way?

First create a shared album: Create shared albums in Photos on iPad

Then add the photos to your shared album.

See: Add and delete photos and videos in a shared album in Photos on iPad - Apple Support (SG)

1. Open the Photos app  on your iPad.
2. Tap the shared album in the Photos sidebar, then tap .
3. Tap all the items you want to add, then tap Add.
4. Type a comment (optional), then tap Post.

When you add new photos, the people you share the album with are automatically notified.

It may take a very long time until you will be seeing the shared photos in the shared albums. Apple is slowing us down, when we are sharing two many items in quick succession: iCloud: My Photo Stream and iCloud Photo Sharing limits

The Shared albums are holding smaller copies of your photos, optimized for sharing or viewing on your  TV. They will be downsized and some metadata stripped for privacy reasons. You cannot use them as a permanent storage of your photos, unless you do not mind to lose quality and metadata. When you add photos to a shared album, the original high quality version will remain in your Photos Library