if you are using Sign Studio and want to use Chromecast 4 as your player, from the downloads page, click on
Custom installation on other vendor devices ( ex. Chromecast, FireStick... ) - there you'd find a full instructions on how to install Sign Player
as part of the instructions, you're to install Chrome on your chromecast before installing the APK. you can find many tutorials explaining how to install Chrome on Chromecast such as this one:
https://www.youtube.com/watch?v=R_ZDjslHmqE - only after you have installed chrome should you proceed to install Sign Player and Sign Watchdog
best regards
-ADMIN