https://wccftech.com/galaxy-s20-120hz-mode-disabled-max-resolution/

Shortly after the leakster Ice Universe confirmed that the Galaxy S20’s 120Hz refresh mode would be available for all three models, he’s back with more news, but this will disappoint most users. Apparently, the 120Hz mode will work on all three versions, but not on all resolutions, unfortunately.

The 120Hz refresh rate model will make every animation smoother than butter, as well as provide a fluid gameplay experience for titles that support the aforementioned refresh rate. However, the display may only refresh 120FPS at the Full HD+ resolution and not the maximum limit, which is WQHD+. Ice Universe hasn’t provided an explanation as to why Samsung would choose this route, but we could have two reasons for it.