No sure I agree on fast. At least on mobile the sidebar has an show/hide slide animation that takes a sizeable fraction of a second. In fact is one of the slowest animations for this I have seen.

I disable animations entirely on devices I use where possible. They just waste time and that adds up if you use something regularly.

I haven't looked at it on mobile, that's unfortunate to hear. I don't see any animation when interacting with it on a desktop browser, snapping open a left side header menu item to see sub-items seems instant.