How to specify parameters in the encoder so that the bitstream_restriction_flag parameter in the SPS of the encoded video in H.264 is set to 1?
You can add vui->bitstreamRestrictionFlag = 1;
See #11131 (Nvenc b_ref_mode middle does not write max_num_reorder_frames == 2 in SPS) – FFmpeg
This is now fixed in ffmpeg. that is way you do it
avcodec/nvenc: set bitstreamRestrictionFlag when neccesary · FFmpeg/FFmpeg@d724584 · GitHub