Even in very simple CRUD projects I have to write a few hundred lines of Javascript to enhance the UI. Stuff like: if you check this box 4 more options appear. Or here is an autocomplete field/dropdown that autofills in 4 other form fields. A lot of basic stuff that cannot be done with raw HTML alone. I can see how something like LiveView would replace the need for mucking around with jQuery when your project doesn't need a big and heavy SPA framework.

Hiding things with unchecked checkboxes, at least, can be done entirely in simple CSS.

  .optional {
      display: none;
  }
  input:checked ~ .optional {
      display: inherit;
  }

I've recently adopted two libraries for my server-side backend app:

1. unpoly to handle common JS behaviours (such as show this div when this checkbox is selected)

2. Web components to handle more complex pieces of UI while maintaining compatibility with LiveView: rendering a functional jQuery carousel via LiveView/Websockets is much harder than just pushing a <carousel> element through the socket. Admittedly I haven't tested if the DOM diffing library LiveView uses plays nice with web components.