Merge pull request #20635 from unoplatform/mergify/bp/release/stable/6.0/pr-20619

docs: Add `DebugSettings.EnableFrameRateCounter` and `CompositionTarget.FrameRate` (backport #20619)

Author: jeromelaban

doc/articles/Uno-UI-Performance.md

@@ -149,6 +149,14 @@ Here's what to look for:
 
 - Use [String Resource Trimming](xref:Uno.Features.StringResourceTrimming) to improve package size and startup time
 
+## Skia Targets Specifics
+
+- On Desktop targets, it's possible to change the composition refresh rate using `FeatureConfiguration.CompositionTarget.FrameRate`. The default value is 60 (frames per second).
+- On all targets:
+  - It's possible to set `DebugSettings.EnableFrameRateCounter` in `App.OnLaunched` in order to view a top-left indicator. It indicates the current frames per second, as well as the time spent rendering a composition frame, in milliseconds.
+  - If the indicator does not change, this means that the UI is not refreshing.
+  - If it is, but nothing is changing visually, it could be that a XAML or Composition animation is still running, see the `ProgressRing` section in this document.
+
 ## Advanced performance Tracing
 
 ### Profiling applications