You navigated here with
fade

A clean crossfade — the safe default.

Declared on this LiveView as: 

use LiveAnimate
@transition "fade"

apply_to

Now click a panel — same LiveView, a live_patch (no navigation):

Panel 1 Panel 2 Panel 3

Showing panel 1 — the patch updates instantly (apply_to: :navigate, the default) — flip the toggle to see it animate.

Top nav = live_navigate (always transitions). Submenu = live_patch (transitions only with apply_to: :all).