Windows not staying maximized when dragged to other monitors
If you turn off Arrange windows automatically by dragging them to the sides or corners of the screen (Aero Snap), you will also no longer be able to drag maximized windows.
To enable dragging maximized windows, start regedit, navigate to
HKEY_CURRENT_USER\Control Panel\Desktop
and set the DragFromMaximize DWORD to 1 to enable.
Reset to 0 to disable.
For more information see the article
Enable or Disable Maximized Window Dragging in Windows 10.