There are no errors at all printed to the console if I launch cin from the terminal.

Just FYI, on a non-Nvidia laptop, you will get the following errors on the terminal where there is no Nvidia graphics card:

[h264_nvenc @ 0x7f0780085a40] Cannot load libcuda.so.1
FFMPEG::open_encoder err: Operation not permitted
int FFMPEG::open_encoder(const char*, const char*):
open failed h264_nvenc:/tmp/testnvenc.mp4

So, it sure looks like "nvenc" is working in Gorge's case.

Also in the nvidia control panel, and I can see this:

But the percentage will hit up to 30-50% many times.