I've made a simple program for Teensy 4.1 microcontroller to send button presses to the Roku over Ethernet. I have posted some sample code at https://forum.pjrc.com/threads/70429-Talk-to-your-ROKU-device-tv-using-Ethernet-) . This should work with any networked microcontroller, but the NativeEthernet library may need to be replaced with ethernet.h .
I am also working some code for making an Accessible Sensitive Touch Button that uses a Joystick and touchscreen display to navigate the Roku. The Roku remotes that come with the Roku devices are difficult to hold for people with limited, and very limited, Range of Motion.