The current Roku OS is 12.5 so you are updated.
https://developer.roku.com/docs/specs/hardware.md also shows the 4230 as still on the "updatable" list. (still receiving updates).
If you are using a SD card, try removing it and see if that helps clear up the display issues. Additionally, have you tried using another HDMI cable or moving the Roku device to another TV (if available) to see if the problem follows the device?