There are plenty of plugins for VS Code that provide this functionality. Take a look at the marketplace https://marketplace.visualstudio.com/vscode. For instance, you could use this plugin https://marketplace.visualstudio.com/items?itemName=xiaoluoboding.vscode-folder-size

In terms of the posible XY problem here, other answer and comments seem to answer the Y, but you seem to still want X. So:

I believe the default VS Code setting search.exclude includes "**/node_modules": true,. If you're really intent on being able to use VS Code's file-content searching facilities to search the contents of node_modules folders, you'll want to define search.exclude explicitly and remove that line from the auto-generated default config.

Note: The reason the default settings are like this is because most people don't usually/ever want to search the contents like that- at least by using VS Code. Including the contents of node_modules in searches can result in much more computational effort, and many more results that those users won't want to see. There may also be search indexing memory-costs. There are other good tools to do file-content searching in folders such as git grep, grep, and ripgrep.