How can I avoid using the jsDelivr CDN?

@AppLEaDay
It possible by following steps -
1. Choose NONE from CDN provider.
2. Download Bootstrap3 and extract on theme root.
3. Update library as below code

framework:
  css:
    theme:
      bootstrap-3.4.1-dist/css/bootstrap.min.css: {}
      css/style.css: {}
  js:
    bootstrap-3.4.1-dist/bootstrap.min.js: {}

4. Cleared cache and refresh page.
5. Now you will get accepted result.

Many thanks, ravi kant! Though I confess at the momentary Iack knowledge about the "libraries.yml" works... may I simply copy your code and paste it inside the libraries file in use beside what it already contains now, no matter what?

@AppLEaDaY
My code can copy but make sure that this type library is already not exist. You may set bootstrap files path in existing library also.

I’m going to close this as an answer has been provided.