To open the User settings:
- Open the command palette (either with F1 or Ctrl+Shift+P)
- Type ">open settings" (You must include the '>' at the beginning)
- You are presented with a few options¹, choose Open User Settings (JSON)
This image was taken in the VS Code online editor

Which, from the manual and depending on platform, is one of:
- Windows
%APPDATA%\Code\User\settings.json² - macOS
$HOME/Library/Application\ Support/Code/User/settings.json - Linux
$HOME/.config/Code/User/settings.json
The Workspace settings will be in a {workspaceName}.code-workspace file where you saved it, and the Folder settings will be in a .vscode folder if and when it has been created.
Official page on User and Workspace Settings
As stated by sevencardz below, VS Code includes a button in the Settings UI gutter which can be used to switch between JSON and graphical view.

The workbench.settings.editor option selects which of the settings files is opened by default when not using the above method, such as with the shortcut ⌘+, or through the application menu.
Footnotes
The aforementioned settings, User and Workspace. Remote settings will appear when using WSL.
By a test this maps to
%APPDATA%\Roaming\Code\User\settings.json, I am not sure by what logic.
To open the User settings:
- Open the command palette (either with F1 or Ctrl+Shift+P)
- Type ">open settings" (You must include the '>' at the beginning)
- You are presented with a few options¹, choose Open User Settings (JSON)
This image was taken in the VS Code online editor

Which, from the manual and depending on platform, is one of:
- Windows
%APPDATA%\Code\User\settings.json² - macOS
$HOME/Library/Application\ Support/Code/User/settings.json - Linux
$HOME/.config/Code/User/settings.json
The Workspace settings will be in a {workspaceName}.code-workspace file where you saved it, and the Folder settings will be in a .vscode folder if and when it has been created.
Official page on User and Workspace Settings
As stated by sevencardz below, VS Code includes a button in the Settings UI gutter which can be used to switch between JSON and graphical view.

The workbench.settings.editor option selects which of the settings files is opened by default when not using the above method, such as with the shortcut ⌘+, or through the application menu.
Footnotes
The aforementioned settings, User and Workspace. Remote settings will appear when using WSL.
By a test this maps to
%APPDATA%\Roaming\Code\User\settings.json, I am not sure by what logic.
On the settings UI page, there's a special button in the top right corner gutter that toggles between the settings.json file and the settings UI.

Bonus Answer:
Add "workbench.settings.editor": "json" to your settings.json file. This will make it so that menu File → Preferences → Settings or ⌘ + , opens your settings.json file by default. Optionally, add a comment at the top to remind yourself where the toggle button is.
// Click the Open Settings (UI) button in the top
// right corner gutter to toggle the settings UI
{
// Other settings in settings.json
// ...
"workbench.settings.editor": "json"
}
Where is settings.json?
I cannot find OpenSettings.json in VScode
Opening settings.json in VSCode - Python - Code with Mosh Forum
VS Code. How to open JSON settings with defaults - Stack Overflow
What is settings.json in VS Code?
What is the fastest keyboard shortcut to open settings.json?
Can I open settings.json directly from my file explorer?
Videos
Hi , I am new to VS Code, doing a python course. The course require to use an extension and change the settings by going and editing the json file. But when I open the settings.json file it is empty. If I click any option in the settings ui, that option is showing in the .json file but default settings are not shown. How do i fix this?
As mentioned @Juraj Kocan in comments, it happens after last VS Code updates.
This is Github issue related to this new "feature"
This one helped me:
"workbench.settings.useSplitJSON": true,
"workbench.settings.editor": "json",
How to Get to the JSON settings in Newer Versions of VS Code
In the latest versions of VS Code, you can convert back to the split JSON settings editor by changing the following settings in the (now standard) UI settings editor:
Workbench > Settings: Editor
- Change from
UItojson
- Change from
Workbench > Settings: Use Split JSON
- Checkmark to enable the option

after making this change, VS Code will open its settings as a JSON file, like in older versions of the application, rather than in the new UI. This allows you to make the changes that other answers provide, directly in the JSON (if you can find the right place and file to make them in..)
NOTE: Whether or not you actually want to use the JSON settings is a different question. Most of the time, the settings search function allows finding the same settings in the new UI. Sometimes it is difficult to get search to work though, especially if the settings are worded differently in the new UI style. There may also be cases where extensions haven't been updated to accommodate the new UI setting style, and so there is no option but to enter the JSON directly.