TradingView Desktop follows your system's theme out of the box. This includes changing the app theme immediately when the system theme has changed, with full support for the Auto mode on macOS.
In case your app's theme shouldn't match your system's setting, you can choose the desired theme manually in the Settings. There are three options:
Changing app theme automatically applies to the chart color theme if a chart template's theme doesn't have any customizations. Otherwise, it won't change and may not match the app's appearance.
Note: You can open the Settings window by clicking your profile picture at the top right corner and selecting Settings or by using shortcut Ctrl+, (Ctrl+<comma>) on Windows/Linux or Cmd+, on Macs.