How do you upload FOLDERS to iCloud?

I'll guess you're trying to do this at iCloud.com in browser.

IMO, each of iCloud's services, while accessible from browser, are best used (with a few exceptions) from the "proper" app.

You can easily copy/paste or drag folders in to the iCloud Drive folder of Finder or File Explorer. They will upload intact.

From a browser, not at all.

Individual files, not folders.

Thanks - it's easy, once you know how.