I've been using the Standard VSCode extension to highlight StandardJS linting errors in some folders in a workspace that has multiple folders representing different repos with different coding styles. It had worked well for over a year, but it stopped showing any syntax highlighting on September 10th, 2021.
I have checked the extension is still enabled and that the standard engine in in my devDependencies and working from the CLI with npx standard.
A recent release changed the default behavior for workspaces with multiple folders. you must now set "standard.enableGlobally": true in your VSCode settings.json or check the related box in the extension settings GUI.