Moxtell When you copy while viewing photo, image content gets copied (as bitmap image, that is why it can be a bit slow). When you paste it in other app, it will create new file with its content.
When you copy from the thumbnail mode, files get copies. When you paste it in other app, like in Windows Explorer, it will physically copy the files from thier original locations. Different applications will behave diferently when you try to paste files, I just tried Faststone, and it would just copy files just like Exporer, but Lightroom classic just ignored it completely.
If your intention is to open files for editing from their original locations, you can use other tool - Open With… - probably that will be better option for you.
As to drag and drop - yes, I as I said, this is in our backlog already.