I have a video file to convert using ffmpeg on Ubuntu 22.04. The input uses the codec h264 and I want to convert it to h265 (mainly for storage capacity reasons). The output of ffmpeg -version is

ffmpeg version N-113725-g37702e2066 Copyright (c) 2000-2024 the FFmpeg developers
built with gcc 11 (Ubuntu 11.4.0-1ubuntu1~22.04)
configuration: --enable-nonfree --enable-cuda-nvcc --enable-libnpp --extra-cflags=-I/usr/local/cuda/include --extra-ldflags=-L/usr/local/cuda/lib64 --disable-static --enable-shared --enable-libx265 --enable-gpl
libavutil      58. 39.100 / 58. 39.100
libavcodec     60. 39.101 / 60. 39.101
libavformat    60. 21.101 / 60. 21.101
libavdevice    60.  4.100 / 60.  4.100
libavfilter     9. 17.100 /  9. 17.100
libswscale      7.  6.100 /  7.  6.100
libswresample   4. 13.100 /  4. 13.100
libpostproc    57.  4.100 / 57.  4.100

I saw online that one of the options of ffmpeg is -threads, but apparently it does not work, since using ffmpeg -i input.mp4 -c:v libx265 -c:a copy output.mp4 and ffmpeg -i input.mp4 -c:v libx265 -c:a copy -threads 2 output.mp4 seem to be exactly the same in terms of CPU usage as shown by htop. Is there something wrong in my usage of -threads?