I have edited photos in LR classic, organised into collections, synced and shared from LR in the browser. When clients download the images, they are very small, so I imagine that's the smart preview as Jim explains in the thread linked below (7MB file downloading as 200KB).
Jim's suggestion is to upload the full size original file from a LRCC client in order to have full sized images available in the albums for clients to download from. I've opened the LRCC desktop client on the same machine as LR classic, but they're already 'in' the cloud (as smart previews only?) and I don't know how to now push the originals up into the cloud from there.
If the full-sized images are 7 MB I'm assuming they are JPEG images. What you probably will have to do is export a full set of JPEG images to your computer that runs Lightroom Classic and then instead of creating a collection and sharing that collection you will have to import those JPEG images directly into Lightroom. Doing that will add the full-sized images to the cloud. You cannot add full-sized images FROM Lightroom Classic.
Yes, Jim. I'm editing raw DMG files in LR Classic but I think it's exported as JPEG to LRCC. Assuming this doesn't allow for any other work around, I will look at implementing your suggestion -- many thanks!
There are c.2000 images over 100 folders for individual clients, so I might just have to add another couple of days to get this done.