Forum type websites are generally required to be SEO-friendly! If your customers do not require high compatibility, consider nextjs in react version or nuxtjs in vue version. On the contrary, you have high requirements for browser compatibility, so you can consider using nodejs as the middle layer (the advantage of this is that your large servers such as java,php remain separate). The worst-case scenario is to add a template engine to the server, such as our common java + JSP.

other recommended solutions: Backbone, Angular, Avalon, etc.

depends on the compatibility requirements of your customers. If you want to be compatible with IE8 or something, you may have to use react. If you want to develop quickly, you can use vue

view layer react + bootstrap4 (redux + react-redux, traffic flow control on ant design), state management