‘Install Apple Silicon’ installs Universal build instead of Apple Silicon-only version on macOS 26.1

Description

When I click “Install Apple Silicon” in the Xcodes GUI, it installs the Universal version of Xcode instead of the Apple Silicon-only build.
This happens consistently on macOS 26.1 with Xcodes 3.0.2 (34).

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Steps to Reproduce
1. Launch Xcodes 3.0.2 on macOS 26.1 (Apple Silicon)
2. Select Xcode 26.1 (17B55)
3. Click “Install Apple Silicon”
4. Wait for authentication and installation to complete

Expected:
The Apple Silicon-only build of Xcode 26.1 should be installed (arm64-only).

Actual:
The Universal version (arm64 + x86_64) is installed instead.

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Environment
• macOS: 26.1 (Apple Silicon)
• Xcodes version: 3.0.2 (Build 34)
• Xcode target: 26.1 (17B55)
• Reproducibility: Always
• Network: Normal (no proxy/VPN)

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Additional Information
• The issue persists even after clearing cache and reinstalling Xcodes.
• The UI label correctly shows “Apple Silicon” in the platform selector, but the resulting installation is Universal.
• The problem does not occur when using the CLI tool (xcodes install 26.1 --platform=applesilicon).

Start by tracing the GUI platform selector's Apple Silicon installation path and compare it with the working CLI command, xcodes install 26.1 --platform=applesilicon. Reproduce on Apple Silicon with Xcodes 3.0.2 and macOS 26.1, then verify that selecting “Install Apple Silicon” installs an arm64-only Xcode 26.1 build rather than the Universal build.