Connecting the Chromecast 2 to WiFi is usefull but also sometimes slow as WiFi coverage isn’t always good in some places of your home. Therefore you can use an ethernet adapter. As an alternative to the expensive Google version, I tried if my own cheap one works.
Turns out, if you use a cheap micro USB splitter from Ebay and an ASIX AX88772b based ethernet adapter it works and you can give the Chromecast the necessary power it needs.
The Chromecast 2 immediately finds the network adapter and starts taking the network connection of that instead of the WiFi module.
It also works on the Raspberry Pi Zero 1.2. Using this splitter will free up a usb port for extra power input if needed, although my 5 volts 2Ah works fine.