Does my Macbook Pro 15" Late 2013 Geekbench 4 score indicate a faulty discrete GPU?
Short Answer

Your discrete GPU is almost certainly fine. The reason for the zero score is that Geekbench is unable to fully test this GPU due to reduced NVIDIA support. Because it can't run a full test, you're getting a score of zero, but this does not mean your GPU is faulty.

Long Answer

According to your Geekbench results, you scored a Depth of Field result of zero because it measured 0.00 pixels/sec for that metric. In other words, Geekbench itself is unable to test this metric, rather than there being an issue with your discrete GPU.

This is a known issue. According to Primate Labs:


  This is due to an issue with the NVIDIA GPU drivers provided with macOS. We’ve contacted Apple regarding this issue and Apple’s response is that they are unable to address the issue due to reduced NVIDIA support. 


Source: Primate Labs Support: Zero OpenCL Score

I did check to see if there were any drivers you could download directly from NVIDIA, but non are available for macOS.

So, unless you're actually experiencing any problems using your MBP, I would just ignore this score altogether.