fix(learn): update guide for v20 (nodejs#8126)

Author: avivkeller

apps/site/pages/en/learn/asynchronous-work/event-loop-timers-and-nexttick.md

@@ -88,6 +88,11 @@ Between each run of the event loop, Node.js checks if it is waiting for
 any asynchronous I/O or timers and shuts down cleanly if there are not
 any.
 
+Starting with libuv 1.45.0 (Node.js 20), the event loop behavior
+changed to run timers only after the **poll** phase, instead of both before and after
+as in earlier versions. This change can affect the timing of `setImmediate()` callbacks
+and how they interact with timers in certain scenarios.
+
 ## Phases in Detail
 
 ### timers