Steam Friends/Chat panel pop-out off screen and cannot be retrieved

Right click the Steam shortcut on the desktop environment and click on Properties. From here, go to the tab at the top called Compatibility and click "Change high DPI settings". Click the checkmark to enable "Override high DPI scaling behavior. Scaling performed by: [Application]."

Thread is old, but wanted to record this for posterity.

This issue happened to me after switching to a 2k display. Although it seems to resize and go off screen in an unreachable area every time I load a game, here's how I was able to manually drag it back in place:

1. Click on the Steam app icon in the taskbar, to make the window active. Obviously, since the chat window is off-screen, don't expect anything to appear.
2. Hover over Steam icon in taskbar. An aero preview of the window should appear above the app icon, just like every other program in Win 10.
3. Right Click on the aero preview, and select Move from the context menu.
4. Your cursor will automatically snap to the window's position and change to the 4-way arrow symbol (the move icon).
5. Press any arrow key once, and then move the mouse without clicking to guide the chat window back on screen.

After you have sight of it again, you can resize it as required.

Fair play to Steam support:

1. Open the Settings panel in the Steam Client by selecting “Steam > Settings” from the top left menu.
2. Select the Web Browser tab.
3. Click on "Delete Web Browser Cache" and then select "OK" to proceed and re-test the issue.

Sorted.

Focus the window, then hold Windows + Shift + Left Arrow or Right Arrow to force Windows to the left or right monitor.