Android (.NET 11): add API 21 Mono fallback instructions

[Copilot]

Summary

Follow-up to #3239, addressing the review comment #3239 (review):

Is there some instruction needed to tell the dev how to fall back temporarily to mono and api 21?

The upstream dotnet/android PR #10753 confirms that API levels 21, 22, and 23 require the Mono runtime — CoreCLR/NativeAOT only supports API 24 and above. This PR adds [!NOTE] blocks in both the What's New page and the Supported Platforms page to explain the temporary opt-out path.

Changes

docs/whats-new/dotnet-11.md

• Added a NOTE admonition to the "Minimum supported Android API" section showing developers how to fall back to Mono + API 21 during the preview period using <UseMonoRuntime>true</UseMonoRuntime> and $(SupportedOSPlatformVersion)=21.
• Fixed the pre-existing </ProperyGroup> typo in the CoreCLR section.
• Updated ms.date.

docs/supported-platforms.md

• Added a NOTE to the >=net-maui-11.0 moniker section stating that Android API levels 21–23 are still supported when using the Mono runtime, with a cross-reference to the fallback instructions in the What's New page.
• Updated ms.date.

Platform notes

• Android-only change.
• The fallback is explicitly framed as a temporary workaround for the preview; developers should plan to migrate to API 24 + CoreCLR for the final .NET 11 release.

Upstream reference

• Add UseMonoRuntime condition to API levels 21, 22, 23 in SupportedPlatforms generator android#10753 — confirms API 21–23 are gated on $(UseMonoRuntime) == 'true'

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Internal previews

📄 File	🔗 Preview link
docs/whats-new/dotnet-11.md	docs/whats-new/dotnet-11

---

Internal previews

📄 File	🔗 Preview link
docs/supported-platforms.md	docs/supported-platforms
docs/whats-new/dotnet-11.md	docs/whats-new/dotnet-11

[learn-build-service-prod]

Learn Build status updates of commit 78b46d8:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/whats-new/dotnet-11.md	✅Succeeded	View (>=net-maui-8.0)

For more details, please refer to the build report.

[learn-build-service-prod]

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[jfversluis]

@copilot also add a note in the supported platforms section, you can refer to this, but mention: lower API levels are still supported if you use Mono.

[Copilot]

@copilot also add a note in the supported platforms section, you can refer to this, but mention: lower API levels are still supported if you use Mono.

Done in cad150e. Added a NOTE to the >=net-maui-11.0 moniker section in supported-platforms.md stating that API levels 21–23 are still supported with the Mono runtime, with a link to the fallback instructions in the What's New page.

[learn-build-service-prod]

PoliCheck Scan Report

The following report lists PoliCheck issues in PR files. Before you merge the PR, you must fix all severity-1 and severity-2 issues. The AI Review Details column lists suggestions for either removing or replacing the terms. If you find a false positive result, mention it in a PR comment and include this text: #policheck-false-positive. This feedback helps reduce false positives in future scans.

✅ No issues found

More information about PoliCheck

Information: PoliCheck | Severity Guidance | Term
For any questions: Try searching the learn.microsoft.com contributor guides or post your question in the Learn support channel.

[learn-build-service-prod]

Learn Build status updates of commit cad150e:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/supported-platforms.md	✅Succeeded	View (>=net-maui-8.0)
docs/whats-new/dotnet-11.md	✅Succeeded	View (>=net-maui-8.0)

For more details, please refer to the build report.