Firstly, you need know that Yarn will not install the client side package to your wwwroot by default.

It globally downloads the package in %UserProfile%\AppData\Local\Yarn\ folder.

In my PC, it exists in C:\Users\username\AppData\Local\Yarn\Cache\v6:

The whole working steps

1. Be sure you have installed note.js, then run following command to install Yarn :

    npm install --global yarn
   

2. Run command to add signalr package:

    yarn add @microsoft/signalr
   

3. Find the signalr package(@microsoft folder) in %LOCALAPPDATA%\Yarn\ and copy the whole @microsoft folder:

   

4. Paste the whole @microsoft folder to your project wwwroot/lib folder:

   

5. Then add the js reference like below:

   <script src="@Url.Content("/lib/@microsoft/signalr/dist/browser/signalr.js")"></script>
   

   

Actually I suggest you can use Libman, it can directly download to your wwwroot folder.

You cannot use the package like that in your Webclient.

Everything you want accessible from your Client must be served by your Server.

Serving a Package is a bit more tricky and I would recommend using a bundler.

With Webpack for example you can prepare your client Resources to be served.

In practice this can look like this:

Webpack is configured to bundle your Client Javascript and put it in <project-root>/assets

Your server is configured to serve every file from the <project-root>/assets directory to the /assets route.

In your client script file you import your library module like so:

import {<your needed parts>} from '@microsoft/signalr';

Finally your html page loads your client script like so:

<script src="/assets/bundle.js" type="module"></script>

This is a simplified example and i would recommend you to read the Webpack docs.