If a newly installed extension in VS Code is not loaded or not showing up, it is probably because the current file is opened in restricted mode in which some extensions are disabled.
Enable trusted mode
If the current workspace is in restricted mode, there will be a message with below contents at the top of the window of VS Code:
Restricted mode is intended for safe code browsing.
Trust this window to enable all features. Manage | Learn More
Then you can click the Manage button in the message banner to enable trusted mode in which all extensions are enabled.
Check which extensions are disabled in restricted mode
If you open extensions view on the left panel, those disabled extensions are displayed with dark color. Check one of them, you will see:
This extension has been disabled because the current
workspace is not trusted.