Starting with MacOS 15.1 there have been a few staff members having issues where when attempting to Chromecast that it won’t. Below is an animated GIF that will show you how to resolve this Chromecast issue. Please be sure to fully quit Google Chrome and relaunch after, don't just click the red circle.
Start by opening "System Settings" from the Apple icon in the upper left corner then watch the animated GIF below.
Fix for if it prompts to allow screen sharing when choosing 'Screen' as a source when Chromecasting:
Quit Google Chrome and try Chromecasting again
Original google doc instructions (permission protected)