Hello, Parrotpeg.
Thank you for using Apple Support Communities! I understand that you have questions about how to confirm that your photo library has been uploaded to iCloud successfully. I'm happy to help.
When you turn on iCloud Photos, the time it takes for your photos and videos to upload to iCloud depends on the size of your collection and your Internet speed. If you have a large collection of photos and videos, your upload might take more time than usual. You can see the status and pause the upload for one day.
On the older iPad, you can check to see if the initial upload has completed if you go to Settings > [your name] > iCloud > Photos. You can also open the Photos app, go to the Photos tab, and scroll to the bottom of your screen.
You can also check your iCloud Photo Library on a computer by visiting the iCloud website: iCloud
For more information about what to expect when you enabled iCloud Photo Library for the first time, check out this article: Set up and use iCloud Photos - Apple Support
I hope this helps! Take care.