So, there is a possibility to shoot HD in 120fps.
I tested 120fps in HD mode (Cinemascope Mode - 1080x850). Camera records KRW codec.
I choose dark scene background for purpose. And I'm not impressed because I find a lot of vertical lines and artefacts. You can also find moire effect here. Maybe because I'm so used to 2K and 4K resolution no and this is "only" HD.