Does this issue occur when all extensions are disabled?: Yes

• VS Code Version: 1.58.2
• OS Version: Lubuntu 20.04

Steps to Reproduce:

1. Create example.geojson with following contents:

{
  "type": "FeatureCollection",
  "features": []
}

2. Open it
3. Note lack of highlighting

Not a duplicate of #89734 #82749 as it was about ability to config it (what is nice that it exists!). And the whole point of VS Code (at least to me) is that it works well out of the box, if I wanted configuring I would use Emacs/Vim

For workaround: File | Preferences | Setting. Search for "file.association"