The upload button does not allow me either to import any video I select, but I could successfully add some videos to my Photos Library on www.icloud.com by sending an iCloud Link to a folder with videos from my iPhone. The iCloud Link appeared in Photos at www.icloud.com and I could add them from there to the library. This helps, when we have two different AppleIDs and want to move videos between two different iCloud Photo Libraries.
What is confusing, however, even after adding two videos, the Media Types section in the sidebar is still not showing an item videos. I have to find them in All Photos.