@Naich
I recommend updating your HTML/CSS first. Many things we used to do in JS are better done now without it (most of animations, many interactions, modals...). And much faster, too.
For replacing jQuery, you can use vanilla JS; it's really, really nice now. Going further, libraries as Alpine can speed your work.
If you want to do something fancier, I recommend Vue. All the power, but easier than React or Angular, and more flexible, from only enhancing HTML with no transpiling to full-blown SPAs with Node, NPM, and all the whistles you may want to avoid at first.