[Problem/Bug]: WAM/WebView2 sign-in: password field renders but accepts no keyboard input (all Office apps, all users) on Canary 29595.1000

What happened?

Summary:
After updating to Canary build 29595.1000 (rs_prerelease, installed 22/05/2026),
the Entra/work-account sign-in surface used by all Microsoft 365 desktop apps
renders the password entry but accepts no keyboard input from any source. The
account picker (Continue / Choose another account) works and is clickable, but
once the password field is shown it cannot be typed into. The previous build,
29591.1000 (18/05/2026), was unaffected.

Repro:

1. Open any Office desktop app (Word, Excel, classic Outlook, new Outlook).
2. At the "You need to sign in" prompt, click Continue.
3. The password entry appears.
4. Attempt to type the password.

Expected: characters are entered.
Actual: the field accepts no input. No characters appear; the field behaves as
if disabled.

Scope / what it is NOT:

• Reproduces in a brand-new local Windows user account (not profile-specific).
• Reproduces across Word, Excel, classic Outlook, and new Outlook (shared
  WAM/WebView2 sign-in surface).
• Physical keyboard AND On-Screen Keyboard (osk.exe) both fail into the field;
  keyboard input works normally everywhere else in Windows.
• Microsoft Edge browsing works normally; only the WebView2-hosted credential
  surface is affected.
• Persists in a clean boot (all non-Microsoft services/startup disabled), so it
  is not third-party software.

Already attempted, no effect:

• WebView2 Runtime repair (setup.exe --repair --system-level --msedgewebview).
• WebView2 Runtime force-update via MicrosoftEdgeUpdate.exe /ua (failed:
  install error 0x80040c01; runtime stays at 148.0.3967.x while Edge is 149.x).
• Office 365 Online Repair.
• Clearing OneAuth / IdentityCache / TokenBroker\Cache and Credential Manager.
• Re-registering Microsoft.AAD.BrokerPlugin and CloudExperienceHost.
• TextInputManagementService confirmed running; ctfmon.exe confirmed running.
• HKLM\SOFTWARE\Policies\Microsoft\Windows\AAD : WebView2Integration = 0 did NOT
  fall back to a working dialog — sign-in then fails outright with no password
  field, indicating no working EdgeHTML fallback remains on this build.

Likely area:
The credential window sets screen-capture protection (SetWindowDisplayAffinity).
This closely matches a previously tracked WebView2 regression where text input
is blocked specifically in capture-protected windows (username/password fields
appear disabled). Suspect the 29595.1000 WAM/WebView2 integration reintroduced
this on capture-protected credential surfaces.

Impact:
Cannot sign into any Microsoft 365 desktop app. Web (office.com) unaffected.
No rollback available (previous build already purged from "Go back").

Environment:
Windows 11 Insider Preview 29595.1000 (rs_prerelease)
Edge 149.0.4022.24 / WebView2 Runtime 148.0.3967.83 (and .70 present)
Microsoft 365 (Click-to-Run), classic + new Outlook installed

Importance

Blocking. My app's basic functions are not working due to this issue.

Runtime Channel

Prerelease (Edge Canary/Dev/Beta), Stable release (WebView2 Runtime)

Runtime Version

148.0.3967.83

SDK Version

No response

Framework

Win32

Operating System

Windows 11

OS Version

29595.1000

Repro steps

I wish I knew...

All I know this issue appeared after the update to the latest version on windows in one of my machines.
In others all is well.

The problem that I have I have is that I cannot fix it, I cannot reset it and thus I cannot use any of the sign on functionality - not even access my Office apps.

Repros in Edge Browser

Yes, issue can be reproduced in the corresponding Edge version

Regression

Don't know

Last working version (if regression)

No response