Githubs performance has been rapidly degrading ever since they started rewriting everything in React. It's basically impossible to view diffs now because they often fail to load, render correctly, or just are incredibly slow.
The root cause of the problem is very fundamental to React and the nature of how the team designed the reactivity model. The TL;DR: React has an inverted model of state management [1].
In Vanilla, Vue, Svelte, Solid, any signals-based reactivity model, you explicitly opt-in to state changes by moving code into your reactive callback. In fact, in almost all of the code that you write, you typically explicitly opt-in to changes in state.
In React, you explicitly opt-out of state changes by moving code out of the reactive callback because the entire component function is the reactive callback (so any state in the path of that function that should not trigger a re-render has to be moved out via a hook).
This fundamental difference is what makes React hard to do well at scale because one needs to be very cognizant of where to place state inside a component and how to optimize for performance with memoization [2] (something Vue and Svelte developers pretty much never think about). The React team spent 2 years building the compiler to automatically manage memoization, but from the benchmarks I've seen, it's hardly made a difference.
In that time frame, Vue has been working on "Vapor Mode" [3] which bypasses the VDOM and brings it to parity with Svelte, Solid, and very close to Vanilla while still retaining a very easy to grok model of reactivity.
[0] https://youtu.be/INLq9RPAYUw
[1] https://chrlschn.dev/blog/2025/01/the-inverted-reactivity-mo...
[2] https://tkdodo.eu/blog/the-uphill-battle-of-memoization, https://tkdodo.eu/blog/the-useless-use-callback
[3] https://www.vuemastery.com/blog/the-future-of-vue-vapor-mode...