VS Code is not detecting problems for some languages with builtin support. Why?

For some reason errors are not producing any code highlighting (red squiggles) or file highlighting (red filenames) in my VS Code when writing in JavaScript and some other languages.

The answer is not apparent, even after a search here, google, GPT, etc. I uninstalled all extensions. Nothing changed. I reinstalled the app, nothing changed. I deleted all referenced to the app, re-installed, and then it worked. Temporarily. Just happened again though, no error highlighting again.

I am writing TypeScript currently, but also not working on JS or TS. errors are working in JSON and Python...

I am currently not running any extension at all, as I uninstalled all for testing purposes. I was using the ES7+ React/Redux/React-Native snippets and a few others.

Any code that would normally produce an error highlight is not.

const someConst = 1;
const someConst = 2;

the above will produce no error highlight in vscode, but obviously not run or compile.

I am running on a Mac with Apple Silicon.

VS Code about:

Version: 1.79.2 (Universal)
Commit: 695af097c7bd098fbf017ce3ac85e09bbc5dda06
Date: 2023-06-14T08:58:52.392Z (2 wks ago)
Electron: 22.5.7
Chromium: 108.0.5359.215
Node.js: 16.17.1
V8: 10.8.168.25-electron.0
OS: Darwin arm64 22.5.0

When I use the Developer: Show Running Extensions command in the command palette, I do not see the "TypeScript and JavaScript Language Features" extension listed.

I'll wager you have some builtin extensions disabled that you don't want to be. Open the Extensions View, and type @builtin into the search bar. Look for extensions that are disabled (they will be displayed dimmer than those that are enabled). For example, check for the "TypeScript and JavaScript Language Features" extension, the "HTML Language Features" extension, and the "CSS Language Features" extension.