WinUI3 apps not running on Windows Insider build 21292.1000

Describe the bug

WinUI3 apps do not run on the latest Windows Insider build (21292.1000)

• Running the app once installed closes immediately it with no prompt
• Running app under debug in VS16.9preview2.0 closes the app and causes VS to restart
• Running app under debug in VS16.8.2 & VS16.8.4 give me this error:

Unhandled exception at 0x7559581E (combase.dll) in App219.exe: 0xC0000602: A fail fast exception occurred. Exception handlers will not be invoked and the process will be terminated immediately.

Steps to reproduce the bug

Steps to reproduce the behavior:

1. Create a new blank app from the templates
2. Try and debug the created app from Visual Studio
3. See crash/restart of VS

Expected behavior

Apps should be able to run

Screenshots

Version Info

NuGet package version: Microsoft.WinUI 3.0.0-preview3.201113.0

Windows app type:

UWP	Win32
Yes	Yes

Windows 10 version	Saw the problem?
Insider Build (21292.1000)	Yes
May 2020 Update (19041)
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Xbox
Surface Hub
IoT

Additional context

[anawishnoff]

This bug has been fixed, and the fix will be available in our next release - WinUI 3 Preview 4. We’re hoping to ship this preview release in early February. Thanks!

[codendone]

The short summary of the cause is that the UDK library failed to properly call through to the OS dll when it should have, which resulted in it not accounting for OS changes on recent insider builds. An automated test was unfortunately missing for this, and a test was added with the fix.

FYI, we are planning to ship a Preview 4 in early-mid Feb., which will include the fix.