From your Photo Library, Select the items that you wish to copy/export to iCloud file storage. When you have selected the items that you wish to copy, tap the Share button (a square with an upward-pointing arrow) at bottom-left of the Library window.
Tapping the Share button will expose an action menu; from the menu select Save to Files - and navigate to the iCloud folder that you have created to receive the exported photos - then tap Save. Your selected photos/videos will be copied to the folder that you have selected.
When you have finished, check that all your photos are visible using the Files App. You should note that photos and videos that are not stored within the Photo Library cannot be accessed or viewed using the Photos App.