Photos

This is only possible, if you stop using iCloud Photos on your iPad. iCloud is syncing your photos across all devices to keep your Photos Libraries on all devices identical to the library in iCloud. So any item you delete on any of your devices will be removed everywhere to keep iCloud Photos identical across all your device. When you are modifying the photos on your iPad, you are modifying them in iCloud, For all purposes, you are working with the same library in iCloud and all your devices.

To save storage for photos on your iPad enable "Optimize iPad Storage" in the Settings > Your Name > iCloud > Photos. Then iCloud will remove high resolution originals from your iPad and replace them by smaller, optimized versions for browsing, if storage is needed and automatically download the originals from iCloud. This is fully automatic. But do not delete photos or videos on your own, that you want to keep in iCloud and your other devices, unless you disable iCloud Photos completely on the iPad, before you delete the photos.

This is explained here in more detail: Use iCloud Photos to store photos in iCloud – Apple Support (UK)