Although jQuery does seem less popular as a choice for new projects nowadays, I'd like to chime in to agree here (not to knock Bootstrap; it's good that they're staying current with their developer ecosystem).
Given appropriate element names and classes, jQuery and CSS selectors can provide a straightforward and readable way to express application behaviours, and it's a well-proven and stable project at this point.
Yeah, this is what some commenters are missing. The real alternative to jQuery isn't some fancy new framework, it's just... plain JavaScript.
Things have really gotten much better in the vanilla world. Although some things remain more verbose or cumbersome than jQuery alternatives, you really don't need a whole layer of abstraction to handle the simple tasks jQuery was designed for any more.
jQuery somehow gets abuse for being more bloated and slower than vanilla js despite the fact that almost nobody is ditching jQuery for vanilla js and instead running to vastly slower and more bloated SPA frameworks.
Given appropriate element names and classes, jQuery and CSS selectors can provide a straightforward and readable way to express application behaviours, and it's a well-proven and stable project at this point.