Roku's run their own operating system. It is NOT Android based. The 4 service buttons on the remote can vary from model to model, country to country, over time, and even variations (4620X, 4620R, etc...)
Basically, the 4620 is very old. It was released in October 2016. Not sure if it's still supported or not. If you want to try and use it anyway, there are power supplies available:
https://www.amazon.com/Premiere-Guy-Tech-Compatible-Replacement-Indicator/dp/B07N67GD9R
https://www.ebay.com/itm/394667382322
If you have supplies laying around, maybe someone here will have the voltage, polarity, and barrel size info you can use to see if you have something compatible.
