[TF2] [Windows 11 24H2] [BUG Report] Issues with display on laptops with multiple displays.

[Mecha-Weasel]

ISSUE:
Issues with display on laptops (and possibly desktops?) with multiple displays.
This issue seems to have started sometime in December 2024.
This issue affects at least two Source-based games.
Definitely affected are both a Valve-produced game (Team Fortress 2) and an independent game (Fistful of Frags).
Of particular note, FoF has not had any updates in many months, it is difficult to picture it being related to any code-change in that game itself.
Unsure if this issue was introduced by recent Steam (beta) update, or recent upgrade to Windows 11 24H2.

OS:
Windows 11 24H2 (recently upgraded).

STEPS:
A laptop (in my case a Dell Latitude with an integrated NVidia GPU) equipped with an external HDMI monitor.
Displays setup in Windows to "Duplicate" (mirror).
External monitor plugged-into HDMI on laptop.
Laptop lid CLOSED.
Launch TF2
NOTE: Also have the same symptom on at least one other Source1 game - Fistful of Frags (FoF).

RESULTS:
On the external monitor a tiny fraction of the screen is displayed on the monitor (looks like maybe the top-left 1/8th of the expected content).
If the laptop lid is OPEN when the game is launched, everything works as expected (game shown normally on both displays).
At which point, the laptop lid may be closed and everything will run as normal for that game-session.
If the game is closed, and launched again with the laptop lid CLOSED, the same problem recurs.

EXPECTED:
Games (examples TF2 and FoF) should display full-screen as normal on the external monitor - regardless of the state of the laptop lid (i.e. open or closed).