.inc is used in various languages. In my case, I use .inc extension in PHP files.
By Default, my vs code editor is not highligthing any code within .inc extension files.
To enable, the highlight option I have done the following steps.
Text Editor Settings
- Go to File > Preferences > Settings > Text Editor > Files > Add Item
- Add entry *.inc > php
- Save

My current VS Code version is 1.74.1