Chromecast or Google TV doesn't show up in Chrome

The Cast list in Chrome is empty or your TV is missing. Checks for Mac and Windows.

Same network. The computer and TV must be on the same Wi-Fi (not a guest network). Mesh systems and 2.4/5 GHz splits are fine if they're one network.
VPN off. A VPN on the computer hides the local network from Chrome.
Mac: Local Network permission. System Settings, Privacy & Security, Local Network: Google Chrome must be on. Without it Chrome can't find any TV.
Windows: network type. Set your Wi-Fi to Private (not Public) so device discovery is allowed, and let Chrome through the firewall.
Restart the TV device and Chrome; then open the Cast menu again (it can take a few seconds to fill).
Router settings. "AP isolation" or "client isolation" blocks devices from seeing each other; turn it off for your home network.

Once the TV shows up, the Chromecast test sends it a short public test video to confirm casting works end to end.