Great that you found this. Here is the homepage of the version we use
https://github.com/ArduCAM/mjpg-streamer/blob/master/mjpg-streamer-experimental/plugins/input_libcamera/README.md<br/><br/>The option isn't even listed there but poking in sources I found this current set of options for libcamer:
fprintf(stderr,
" [-c | --camera ].......: Chooses the camera to use.\n"
" [-f | --fps ]..........: frames per second\n" </div>
" [-b | --buffercount ]...: Set the number of request buffers.\n" </div>
" [-q | --quality ] .....: set quality of JPEG encoding\n" </div>
" [-rot | --rotation]....: Request an image rotation, 0 or 180\n"
" [-s | --snapshot ] .....: Set the snapshot resolution, if not set will default to the maximum resolution.\n" </div>
" ---------------------------------------------------------------\n" </div>
" Optional parameters (may not be supported by all cameras):\n\n"
" [-br ].................: Set image brightness (integer)\n"</div>
" [-co ].................: Set image contrast (integer)\n"</div>
" [-sa ].................: Set image saturation (integer)\n"</div>
" [-ex ].................: Set exposure (integer)\n"</div>
" [-gain ]...............: Set gain (integer)\n"
" [-afmode]..............: Control to set the mode of the AF (autofocus) algorithm.(manual, auto, continuous)\n"
" [-afrange].............: Set the range of focus distances that is scanned.(normal, macro, full)\n"
" [-lensposition]........: Set the lens to a particular focus position, expressed as a reciprocal distance (0 moves the lens to infinity), or \"default\" for the hyperfocal distance"
" ---------------------------------------------------------------\n\n"</div><div> );
but no hdr. Not sure if with video streams hdr is also available. I could think that for still images it uses several snapshots with different exposure to create it.