Around 2 minutes or so of watching anything, this weird promotional display will pop up on the side. It keeps saying “RCA | Roku TV” at the top, then 5 icons that follow down the left side of the screen, and it’ll tell me about each one with a white box next to it. Basically going over everything the TV can do in a simplified form. Is there any way to turn this off?
You need to go into the TV's settings and turn off something possibly labeled "store mode" or "demo mode".
I did a quick search for a manual online, and it seems the only way to get out of store mode is to factory reset the TV:
Press OK to select Set up for home use. This is the right choice for enjoying your TV at home. It provides energy saving options as well as access to all features of the TV.
Note: Store mode configures the TV for retail display and is not recommended for any other use. In store mode, some features of the TV are missing or limited. To switch from one mode to the other, you have to perform a factory reset as explained in Factory reset everything, and then repeat Guided Setup.