I am assuming you are referring to a 120 Hz refresh rate. Just because a TV says it has a specific refresh rate, that doesn't mean it can accept a video signal at that rate. That rate is what the display operates at, and often uses software manipulation to display that rate.
My laptop is connected to my Sharp Roku TV via HDMI. I don't know what the specs claim for my display, but my laptop is reporting 60Hz output, and doesn't have any higher refresh rate available. And my laptop has a pretty high end video card. That's likely the highest refresh rate accepted by the HDMI port.
Dan
Roku Community Streaming Expert
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