App URI Handler (HTTPS deep linking) works with local sideload but not with Microsoft Store flight package

Question

I'm implementing App URI Handler (Web-to-App linking) for a Flutter Windows (MSIX) app and have hit a distribution-specific issue after extensive testing.

Environment:

• Windows 11, Flutter Windows desktop app packaged as MSIX
• Domain: app.xxx.com, hosting .well-known/windows-app-web-link with correct packageFamilyName and paths
• Manifest includes:

XML
<uap3:Extension Category="windows.appUriHandler"> uap3:AppUriHandler <uap3:Host Name="app.xxx.com" /> </uap3:AppUriHandler> </uap3:Extension>

✅ What works: Sideloading the app locally with a self-signed certificate (same package identity, publisher, and domain as the Store submission) — clicking https://app.xxx.com/... links via Win+R, Outlook, or Teams opens the app directly, with no browser and no popup. The app also correctly appears under Settings → Apps → Default apps → https.

❌ What doesn't work: The identical package, submitted and installed via a Microsoft Store flight (Partner Center), does not trigger the same behavior:

• Clicking the same https://app.xxx.com/... link opens the browser instead
• The app does not appear under Settings → Apps → Default apps → https at all
• Verified: correct packageFamilyName, no redirects on the hosted .well-known file, clean uninstall/reinstall tested, waited several hours for background verification

Question: Since every configuration variable (manifest, domain hosting, package identity) is confirmed identical and correct between the two tests, is App URI Handler domain verification (CDA) not supported for flight-distributed packages? Does this require a public or audience-targeted Store release to trigger properly? Any documentation or guidance on this specific gap would be greatly appreciated.