Welcome to the forums. 
Here are a few alternatives to get your screencasting working on Debian:
1. Using scrcpy for Chromecast
You can try using scrcpy, which is a versatile tool that mirrors Android devices. Although it’s primarily used for Android mirroring, it can be combined with a Chromecast dongle or Google Cast-enabled smart TV. Here’s how:
Install scrcpy:
sudo apt install scrcpy
Connect your Android device to your TV using Chromecast, then mirror your Debian desktop to your Android device through scrcpy.
2. Using VLC for Chromecast
VLC media player has a built-in Chromecast feature that can help you stream media to your TV.
Install VLC:
sudo apt install vlc
To cast your screen:
- Open VLC.
- Go to Playback > Renderer > [your Chromecast].
- Use VLC’s screen capture option to mirror your desktop.
Note: This might not be as fluid as a dedicated screen mirroring solution, but it can be an alternative.
3. Using Gnome Network Displays for Miracast
If your TV supports Miracast, you can use Gnome Network Displays to cast your screen wirelessly.
Install Gnome Network Displays:
sudo apt install gnome-network-displays
After installation, launch the application:
gnome-network-displays
Follow the prompts to connect to your TV if it supports Miracast.
4. Using KDE Connect
If your TV has an Android TV OS, you can install KDE Connect both on your Debian machine and on the Android TV to cast the screen.
Install KDE Connect:
sudo apt install kdeconnect
Then install KDE Connect on your Android TV from the Google Play Store and follow the pairing process.
If you try any of these methods and run into further issues, feel free to share the error details, and we can troubleshoot it together.