A:Answer No, you cannot change the refresh rate from 60 to 120.
This TV does not have 'true' 120hz refresh rate; specs list it as having true refresh of 60hz and 'motion enhancement technology' (Motion Enhancement Technology
Every TV has a native refresh rate (the Hz shown), an important factor in motion clarity. In addition to refresh rate, look for proprietary technologies that help deliver smooth, seamless pictures.).
TCL support explains: https://support.tclusa.com/20269-roku/189407-why-does-the-product-description-say-the-tv-is-120hz-but-the-specifications-say-that-it-is-60hz
This article by CNET provides more in-depth answer into this question: https://www.cnet.com/news/ultra-hd-4k-tv-refresh-rates/
I have this model and do a lot of gaming (PS4 & Xbox1) and have not noticed any issues with image lag.