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.
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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.