Front-end is harder than back-end

Or convince me otherwise. I thought this would lead to an interesting discussion. I'm a back-end developer, currently constructing a front-end app in ReactJS. Ok, I must say I'm a newbie when it comes down to ReactJS. But as an example, it took me 20 minutes to realize that a table with 1000 elements, each having edit buttons, led to the slow response of displaying a modal. Now, I'm tasked with finding an effective solution to address this issue—whether it's through pagination, using react-window, or exploring other alternatives. And I haven't even found the cause whether it's the amount of event handlers, the size of the virtual DOM or something else. Back-end feels so much straightforward.