[FIX] TypeError: $(...).once is not a function

And look for 2x defined jquery in your code.

Unless specified, your theme does not use jquery.once as dependency. This can result in and error TypeError: $(...).once is not a function when using BigPipe, where you just need .once() function as salt.

  dependencies:
    - core/jquery
    - core/jquery.once

So the whole file can be somehow like:

framework:
  css:
    theme:
      css/select2.min.css: {}
      css/style.css: {}
  js:
    js/select2.full.min.js: {}
    js/scripts.js: {}
  dependencies:
    - core/jquery
    - core/jquery.once

Remember, YAML files are space-sensitive!