Really wish Roku would add an app for Android TV (e.g., Nvidia Shield) streaming devices. I tried to watch WEIRD this weekend and I cannot tell you how difficult it was to get it to work on my Sony TV (Android TV) and Nvidia Shield via Chromecast. Even Apple TV+ eventually came around and realized if you're going to be in the streaming business, you need to allow people to stream from all types of devices...even if they're competing devices.
What was your solution? I'm having the same issue.
I ultimately had to use a laptop/desktop computer with the Chrome browser and chromecast it from there. Not ideal and you lose the surround sound (if it's there to begin with) doing that -- but it worked.