We my cloud is just a very simple (and not very reliable but I digress) NAS server. You can definitely have images on it and access them through Lightroom Classic. When you copied them over and tried to import them, Classic recognized it already had these images in their original location and refused to import them. This is in general NOT how you move images or backup images with Classic. You can offload images to a network drive such as this thing if you want using the process described here: https://www.lightroomqueen.com/move-photos-another-hard-drive-leaving-catalog/
the process is identical for network drives. If you use any other method, you WILL lose your edits as already mentioned. Lightroom Classic is just a catalog that points to files on your hard drive, external or network drives. If you move files outside of Classic it loses the connection and you will have to relink the images. Make sure you have another backup before you do any of this. As also said, if your images are not in two places simultaneously, you do NOT have a backup.