Just wanted to let people know that it is possible to install Zwift using the APKpure app in the Nvida Shield (maybe other Android TV boxes too). You’ll have to download and install APKpure (either download the apk to a pc and transfer via usb drive, or download from a web browser in the Shield).
You’ll also need ES File Explorer and Sideload launcher (both of these are in the Play store). ES File Explorer is for installing the APKpure app (you may have to allow ES explorer to install third-party apps), and once it is installed you have to use the Sideload launcher to run APKpure.
Once in APKpure (it is like an appstore for free apps), you can search for Zwift (it is the one that says unreleased). Then download and install it from there (and you’ll probably have to allow APKpure to install apps from third-party sources).
Once Zwift is installed, you’ll have to run it from the Sideload launcher. I confirmed that it ran, and I was able to log in, and pair my trainer.
The downside is having to download and install a third-party app store. But the upside is that you don’t have to worry about copying the .obb directory each time you install and update.