The security impact relates to the fundamental design architecture of the lock screen.
Similar to iOS Before First Unlock (BFU) security mechanisms being stronger and less capable overall, so too do you see this behavior on Windows.
The user mode lock screen is simply a full screen app, for which glitching the resolution of an “external” monitor which video out ports is often enough to desync the resolution of the full screen lock screen app and the full logged in user desktop behind it. IE: you can just… click past the lock screen app briefly running at a smaller resolution. As you might imagine, there’s a timing aspect to this.
That’s why this behavior exists.
