Sort of on a tangent to the actual content of the page, but what documentation system/CMS is this particular web page UI? It seems very fast and relatively uncluttered for the menu on the left side, content pane, top horizontal menu bar.
If I'm understanding this codebase right, it's a hand-rolled framework based on MDX and Next.js; the UI elements you're referring to were designed from scratch and aren't based on any existing CMS theme.
I disable animations entirely on devices I use where possible. They just waste time and that adds up if you use something regularly.