Topic on Talk:The Invincible
Bit depth of back buffer doesn't have much to do with HDR displays either. Most games render into FP10 or FP16 back buffers these days - this is needed for "in-game HDR", the one which was introduced back in 2014 or so with Far Cry and HL2 Lost Coast.
I've checked and the game doesn't do anything to display color, stays at 8 bits on my C1. So it's safe to say that the game doesn't support HDR.