Even though I'm a fan of React, and use it for practically every web application I build, my biggest and most obvious issue has been that writing UIs through React doesn't feel as natural as, say, writing command line tools in Go, or live/realtime apps in Elixir.
Some languages just feel incredibly natural and frictionless for certain things, and nobody has really nailed UIs yet. Swift, JSX/HTML, Svelte, or whatever framework of the week: they all feel like they're working around the problem to some extent. Like at some point in the process, the designers of the language/framework had to compromise and implement some hacky/weird/painful syntax to satisfy project requirements.
UI's natural interface is visual, so tools like Figma can serve as an essential part of the solution, but nonetheless, I feel there's something missing. There must be a more intuitive way to represent the visual through code. The current solutions, although I find it hard to describe precisely, are always tantalizingly lacking in one way or another.