Document Mono project properties breaking change for mobile apps

docs/core/compatibility/11.md

@@ -109,6 +109,7 @@ See [Breaking changes in EF Core 11](/ef/core/what-is-new/ef-core-11.0/breaking-
 | Title                                                             | Type of change    |
 |-------------------------------------------------------------------|-------------------|
 | [Minimum Android API level raised to 24](maui/11/android-minimum-api-level.md) | Behavioral change |
+| [Mono project properties no longer configure mobile apps](maui/11/mono-project-properties.md) | Source incompatible/behavioral change |
 
 ## SDK and MSBuild
 

docs/core/compatibility/maui/11/mono-project-properties.md

@@ -0,0 +1,78 @@
+---
+title: "Breaking change - Mono project properties no longer configure mobile apps"
+description: "Learn about the breaking change in .NET 11 where Mono project properties no longer configure mobile apps."
+ms.date: 10/21/2026
+ai-usage: ai-generated
+ms.custom: https://github.com/dotnet/docs/issues/56477
+---
+
+# Mono project properties no longer configure mobile apps
+
+In .NET 11, Mono project properties no longer configure mobile apps.
+
+## Version introduced
+
+.NET 11
+
+## Previous behavior
+
+The following Android settings controlled Mono AOT, LLVM, profiling, or the
+Mono interpreter:
+
+- `RunAOTCompilation`
+- `AotAssemblies`
+- `EnableLLVM`
+- `AndroidEnableProfiledAot`
+- `AndroidAotMode`
+- `AndroidAotAdditionalArguments`
+- `AndroidExtraAotOptions`
+- `@(AndroidAotProfile)`
+- `AndroidAotEnableLazyLoad`
+- `AndroidUseInterpreter`
+- `UseInterpreter`
+
+`AndroidEnableMarshalMethods` isn't Mono-specific, but .NET 10 Android projects
+could use it with the previous code-generation pipeline.
+
+The following Apple settings controlled the Mono interpreter, SGen garbage
+collector (GC), LLVM, float handling, interface layout, or Mono AOT:
+
+- `UseInterpreter`
+- `MtouchInterpreter`
+- `EnableSGenConc`
+- `MtouchEnableSGenConc`
+- `MtouchUseLlvm`
+- `MtouchFloat32`
+- `MonoUseCompressedInterfaceBitmap`
+- `RunAotCompilation`
+- `AotAssemblies`
+- `AotCompileMaxDegreeOfParallelism`
+
+## New behavior
+
+The Mono-specific settings don't provide their previous behavior on CoreCLR.
+Some settings have no effect. Others cause a build warning or error.
+
+`AndroidEnableMarshalMethods` can't be combined with ReadyToRun. This
+combination causes build error `XA1049`.
+
+## Type of breaking change
+
+This change can affect [source compatibility](../../categories.md#source-compatibility) and [behavior](../../categories.md#behavioral-change).
+
+## Reason for change
+
+Most of these settings configure Mono components that aren't used by CoreCLR.
+`AndroidEnableMarshalMethods` is included because its previous build
+configuration isn't compatible with the CoreCLR ReadyToRun path.
+
+## Recommended action
+
+- Remove the Mono-specific settings from .NET 11 projects, or set them only for
+  .NET 10.
+- Don't enable `AndroidEnableMarshalMethods` in a CoreCLR ReadyToRun build.
+- Retest the app's performance and memory use.
+
+## Affected APIs
+
+None. This change affects MSBuild properties and items.

docs/core/compatibility/toc.yml

@@ -108,6 +108,8 @@ items:
             items:
               - name: Minimum Android API level raised to 24
                 href: maui/11/android-minimum-api-level.md
+              - name: Mono project properties no longer configure mobile apps
+                href: maui/11/mono-project-properties.md
           - name: SDK and MSBuild
             items:
               - name: dnx scripts bypass global.json SDK selection