It seems I can COPY the cells by selecting one and then Shift+Down etc ... check marks appear on all the cell, I can copy it, but then pasting just dumps everything into one cell. And I think the ObservableHQ model is some weird single await per cell. You can not have more than "one line" of code per cell.
How to paste?
When you copy multiple cells, the clipboard holds different versions for different contexts:
If your keyboard focus is inside a cell editor in another notebook, the clipboard treats that as a plaintext context, so it'll just paste the code all lumped together.
To paste the cells as cells, press Esc so that a blue border appears around the cell (the same kind of focus state in which you originally selected the cells) and then paste.
(I work at Observable; copying and pasting cells is a new feature, and we could probably improve it with some auto-detection.)