I have about 55k photos in my LrC folders and I also transitioned the catalog to Lr some many years ago. I use both depending on where I am and what I need to do, as rthey have some different features. I have gone on adding photos in both places depending or not whether I was at my Mac or not. I have a creative cloud subscription, and am nowhere near out of space.
My problem/concern is that when I load a photo in LrC, it seems that only a smart preview is loaded to the cloud. If I want to abandon LrC altogther and just use Lr going forward, how do I make sure all my LrC originals are loaded into the cloud and are not duplicated if there are files already there.