Is there a secret menu to reach some settings like dynamic contrast, refresh rate, "just scan", black levels, gamma settings, etc...?
When video is playing full screen, press the * button to get to some more advanced picture settings (a lot more than are available in the main Settings menu). They are remembered per input, so you'll need to adjust them for each.
Lastly, 120hz seems to be false advertising, I see nothing above 60hz. I guess it is some of this new "effective refresh" nonsense?
Precisely that... per TCL: "TCL Roku TV's use a combination of advanced signal processing and back light scanning to enhance the native refresh rate of the LCD panel (60Hz or 60 frames per second) and present an effective refresh rate (what your eye sees) of 120Hz, or 120 frames per second. This accounts for the way the TV is listed. The result is a smother (sic), blur free image, perfect for fast moving sports or video games."