Is this connected to a non-4K tv? It sounds like the Roku is sending a 4K signal to the TV but the TV can only display part of it.
If you can see the screen options well enough to navigate:
Settings > Display type
When you change the Display type to a new setting it runs you through several screens:
- A screen where you can choose from the available options on that device.
- A screen where it analyzes your choice to be sure your tv supports it, then gives the option of trying that choice if you wish.
- A screen with a countdown timer and two choices:
Yes, screen looks good
No, I will choose a different setting
The "No" option is highlighted by default. To keep the screen resolution you're currently trying, you need to arrow up to the "Yes" option and click on it before the timer runs out.
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
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Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X