Bootstrap Studio allows you to link external JS files without importing them. This can be useful if you want to include things like JS libraries. They are not stored as files in your project, instead they're included in
<script> tags before the page's closing
Then you need to enter the url of the file you want to link in your project and click the "Import" button.
Keep in mind that Bootstrap Studio caches external JS files for some time. If you want to get the latest version of the linked file, you need to right click it, and choose the "Refresh" option.
The Link External feature is a great way to include libraries hosted on a CDN like cdnjs.