Material nodes not working?

Hi so I’ve been trying to assign materials to my objects but then nothing happens.
I took a closer look at the nodes and they just show a black square. The objects only show the default squares.
My materials aren’t wrong because I tested with only putting in one constant3vector with a random colour with the output on base colour but this is showing up as black in the node and default grid on the object too.
How can I see my materials?
I’m using a Mac, and Xcode recently updated, which I think is affecting things.