One of the Microsoft Windows keyboard shortcuts I have used since the earlier 1990s is the Alt-F4 combination. It simply closes the current window so you don’t have to use your mouse to click on the X in the corner. To execute the command, hold down the Alternate key which is labeled “Alt” on either side of the space bar. Then tap the F4 key on the top row of the keyboard. Whatever window is current will close and if you hold the Alt key down and tap the F4 key the next window will close in succession. If work needs saved in the closing window, you will be prompted to save or cancel.
This shortcut has been around since Microsoft Windows 3.1 and still works in Windows 10 and every version in between. It even works in Linux Mint for some programs.
If you aren’t already, try the alt-F4 keyboard shortcut when you want to close an open window and see if it’s quicker than the mouse.