Unfortunately due to limitations to ChromeOS, Videostream cannot integrate with Chromebooks. The exploit by which we facilitate the cast is blocked on ChromeOS, so the fundamental way Videostream can stream to Chromecasts is impossible.
While Chrome apps will be discontinued on Windows, Mac, and Linux, it would stay operational for ChromeOS until June 2022.
The edition of our app that works is on the Chrome store here: https://chrome.google.com/webstore/detail/videostream-for-google-ch/cnciopoikihiagdjbjpnocolokfelagl?hl=en
Cheers!