All of this can be done quite efficiently on a native widget. The problem with Notion is that it uses Electron.
It's a fun meme to blame Electron for everything but the problems with Notion are obviously with its state and data management. Booting/rendering performance is not the bottleneck here, and having used lightning fast Electron apps, I'm sure it never will be.
Put differently: what measurements do you have of the performance issues of Notion and is Electron performance the root problem of them?
Compare it with the few MBs needed by an equivalent native app with exactly same functionality.
By any standard and by any metric, Electron is bloated. Some applications (like VSCode) can disguise it quite well and give a an acceptable user experience.
Text Rendering, CSS Layouts, Accessibility, being good at cross-platform, Canvas/WebGL and a myriad of other APIs make Electron pretty powerful. I don't know exactly, but I think QT would be it's main competitor when it comes to those features. But QT isn't always that easy to develop with.
Here you are complaining that a "hello world" uses a lot of memory. Yes, that's true, but the use case for Electron is not to display just "hello world", it's to build full, accessible applications in languages who are usually native on the web.
What counts is the final user experience.
There is a level of optimization where that is relevant and it's relevant in a bigger context of responsible resource usage but that's not what we're talking about here.
This was exactly my point as to the "memes" of Electron criticisms, your point is completely off topic but because someone mentioned "Notion" someone has to make your point nearly verbatim every time.
It does not add anything valuable to the discussion. Talking about caching strategies, offline/online functionality and layout thrashing is much, much more interesting here.