Xcode 26.6 cannot download iOS 26.5 Simulator runtime — stuck on “Preparing…”

I am unable to download and install the iOS Simulator runtime in Xcode 26.6.

Environment:

MacBook Air with Apple silicon macOS Tahoe 26.6 Xcode 26.6 Build version 17F113

xcode-select -p:

/Applications/Xcode.app/Contents/Developer

xcodebuild -showsdks correctly reports:

Simulator - iOS 26.5 -sdk iphonesimulator26.5

However:

xcrun simctl list runtimes

returns:

== Runtimes ==

No Simulator runtime is installed.

In:

Xcode > Settings > Components

I attempted to install:

iOS 26.5.1 + iOS 26.5 Simulator

but it remains at:

Preparing...

for a very long time without actually downloading the runtime.

I also tried:

xcodebuild -downloadPlatform iOS

This eventually failed with:

Download was cancelled exit code 70

I also tried:

xcodebuild -downloadPlatform iOS -exportPath ~/Downloads/XcodePlatforms

The destination directory remains at 0 bytes.

Checks already completed:

• More than 860 GiB free disk space
• Mac restarted
• Xcode quit and reopened
• xcode-select points to the correct Xcode installation
• /etc/hosts contains no Apple blocking entries
• gdmf.apple.com resolves correctly
• HTTPS connectivity to gdmf.apple.com works
• Apple MobileAsset / software update services are running
• iOS Simulator SDK itself is installed correctly

The project can compile for iphonesimulator26.5, but Simulator execution and tests are blocked because no runtime can be installed.

Questions:

1. Is this a known issue with Xcode 26.6?
2. Is there an official alternative way to download the iOS Simulator runtime?
3. Can I install an earlier supported iOS Simulator runtime instead?
4. Is there a MobileAsset or Xcode cache reset procedure recommended by Apple?

Thank you.