System theme setting does not persist or update correctly on system theme change

[vatsashah45]

Current behavior

When the app theme is set to System Theme, it correctly switches to Light mode when the system theme is changed to Light
However, when the system theme is later changed back to Dark, the app stays in Light mode

And, the settings UI incorrectly displays Light as the selected theme instead of System Theme

Screen.Recording.2025-07-31.at.3.30.59.PM.mov

Expected behavior

When the app is set to follow the system theme:

• It should switch to Dark mode when the system theme is changed to Dark and vice-versa
• The settings UI should continue to display System Theme as the selected theme unless explicitly changed by the user

How to reproduce it (as minimally and precisely as possible)

1. Open the Chefs app and set the theme to System Theme
2. Change the system theme from Dark to Light → app switches to Light (correct behavior)
3. Change the system theme from Light to Dark → app remains in Light mode (incorrect)
4. Observe that the settings screen shows the "Light" theme as selected (also incorrect)

Uno Version(s)

• Uno.Sdk Version:

Affected platform(s)

• iOS
• Android
• WebAssembly
• WebAssembly renders for Xamarin.Forms
• Windows
• Desktop
• Build tasks

Relevant plugins

• Resharper (version: )

Anything else we need to know?