(1) It is easier to use plain JS to do a lot of things than it was when jQuery came out. Also there are alternatives that are more declarative like HTMX and that thingie in bootstrap that makes data-toggle work [1]
(2) I find it a little nerve-wracking for a React application to have some set of things that are really managed by React (e.g. you change a state variable and it redraws a view) as opposed to, say, use jQuery to set a CSS class that, say, shows or hides something. I wish the state was all in one place as opposed to partially in the React state and partially in the DOM. However, just touching the CSS class directly is super-fast and CSS transitions and animations work exactly the way you want for many things that way.
[1] https://stackoverflow.com/questions/30629974/how-does-the-da...