I suspect your confusion is because you are trying to use copper cable item (one that is crafted inside of assembling machines that is used for crafting green chips). This is not the item you want to use for manually adding copper wires now. In the shortcut bar there is a "make green wire"...

So I just got the new Space Age DLC and if I remember correctly before that I could just click on two electric poles to manually wire them (like here https://wiki.factorio.com/Copper_cable). I still can disconnect them using shift+left click, but can't connect them back. When I try to left click on ...