Funny how reasonable performance is now treated as some impossible lost art on the web sometimes.
I posted a little clip [1] of development on a multiplayer IDE for tasks/notes (local-first+e2ee), and a lot of people asked if it was native, rust, GPU rendered or similar. But it's just web tech.
The only "secret ingredients" here are using plain ES6 (no frameworks/libs), having data local-first with background sync, and using a worker for off-UI-thread tasks. Fast web apps are totally doable on the modern web, and sync engines are a big part of it.