Try this command line and adjust as necessary
Code:
"C:\Program Files (Portable)\NVEncC\NVEncC64.exe" --vbrhq 38400 --codec h265 --preset quality --profile main10 --level 5.1 --output-depth 10 --ref 5 --gop-len 24 --lookahead 32 --qp-init 1 --max-bitrate 38400 --vbr-quality 25 --aq --cuda-schedule auto --mv-precision q-pel --cabac
Note that different NVidia cards have different capabilities
If you a RTX 20xx type you can use b frames