For disabling Chat-related AI features of VS Code, use the chat.disableAIFeatures setting.
Specific features for GitHub Copilot
See the official enable/disable docs. TL;DR, pre-1.97 there's a status bar indicator for GitHub Copilot in VS Code, and upon clicking it, you will be prompted to disable it globally or just for the specific language mode of your currently active editor tab (see the github.copilot.enable setting, which takes an object mapping language modes to booleans for whether Copilot should be enabled for editor tabs in the language mode). Post VS Code 1.97, I think that thing has moved to the title bar and is visible even without the extension installed, and I believe that can be hidden using the chat.commandCenter.enabled setting and right clicking the other copilot action buttons in the title bar and hiding them.
There's also a command you can bind to a keyboard shortcut: github.copilot.completions.toggle (previously github.copilot.toggleCopilot). That's the command ID; the command title which you can use in the command palette is GitHub Copilot: Enable/Disable Copilot Completions.
For excluding files from GitHub Copilot, see How to Exclude Specific Files (like .env) from GitHub Copilot in VS Code?.
You may also be interested in [Idea] AI actions should respect Copilot Completions language disablement #199379.
If you just want to disable automatically showing inline completions, then use the github.copilot.editor.enableAutoCompletions setting.
General disablement of VS Code extensions
To disable an extension, go to the extensions view. You can do that under the "View" menu at the top left, or click the icon at the left bar, or use the View: Show Extenstions command, or ctrl+shift+x (on Windows and Linux).
Here are pictures of the extension button icon that you can see in the left bar:

Then scroll until you find the Github Co-pilot extension, then click the gear icon at the bottom right of the extension card. Then, in the menu that pops up, click "Disable" or if you only want to disable it for the current workspace, "Disable (Workspace)".
Here are pictures of the gear button icon that you can see at the bottom right of the extension card:
