Since none of the answers really give an answer to the original question, is there a way to view automatically prettified JSON in Visual Studio Code, I'll here provide a workaround that may help if one has tons of JSON to view that are not prettified. This workaround presents a method to Prettify all of them at once.

VSCODE Prettify multiple JSON files trick, no extensions or plugins needed
(tested on MacOS, VSCODE Version: 1.105.1)

1. Open Visual Studio Code (VSCODE)

2. Select the Preferences: Open User Settings (JSON) command in the Command Palette using shortcut - ⇧⌘P

3. Check that under JSON section there is setting - "editor.formatOnSave": true,

   "[json]": {
                   "editor.defaultFormatter": null,
                   "editor.formatOnPaste": false,
                   "editor.editContext": false,
                   "editor.formatOnType": false,
                   "editor.wordWrap": "on",
                   "editor.formatOnSave": true,
                   "files.autoSave": "off"
               },
   

4. Modify the - settings.json - file if necessary, save and close it.

5. Drag the folder that has multiple not prettified JSON files into middle of VSCODE window.
   NOTE! It's recommended to take a backup copy of this folder in case you make a mistake in following these instructions.

6. If file Explorer doesn't appear automatically for some reason, open it from the top left symbol that has two papers on top of each other

7. Click on the first JSON file on the list and its contents should appear on the right panel

8. Use keyboard shortcut - ⌘A - to select all the files on the list

9. Close the just opened file on the right panel ( X symbol after the name tab), if there is any files with contents visible, those files will not be prettified.

10. Click the magnifying glass symbol on left side of the window

11. Type on both fields just plain comma  -  ,  - (without these lines or other characters), since commas are found in every JSON document

12. Click -  .* - symbol at the end of the first line where you placed the comma, multiple search results should appear below these fields

13. Click then a symbol below that -  .* - symbol, it should show a hover text - Replace All - on top of it when you move your cursor on top of it

14. Answer to the question replacing those commas with similar commas - Replace - after which there should be a message at the upper left corner saying something like - Replaced XXX occurences across XX files with ','.

15. Click the Explorer symbol above the magnifying glass and select any file from the list to see that it should be now prettified. VSCODE has saved them all, too (even though - files.autoSave - variable above in the settings has been turned off.

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