If your ESO client freezes/crashes in Windows 10, you do not need to restart your system nor log off the current user to fix it.
Just follow the steps below to close the client.
Any of the images may be clicked on to view at full-size if needed.


STEP 1:
To start the process - on your keyboard - simply hold the WINDOWS key and press TAB. (WIN+TAB)


STEP 2:
In the upper-left corner, click the New Desktop button.


STEP 3:
At the top of your screen, you will see your new Virtual Desktop.
Click on your new Virtual Desktop to bring it to focus.


STEP 4a:
After entering your new Virtual Desktop, you will need to bring up the Task Manager.
The easy way to do this - on your keyboard - is by holding CTRL and SHIFT at the same time, then pressing ESC. (CTRL+SHIFT+ESC)

You will either be greeted with this version of Task Manager, or the one in the picture below.
Either of these Task Manager windows will work, as the process for terminating the ESO client is the exact same!


STEP 4b:
Left-click on the ESO app to highlight it in the Task Manager, then click click the End Task button in Task Manager.
This will force ESO to close on your main desktop. You may now close the Task Manager window, or proceed to Step 5.


STEP 5:
Once more, press WIN+TAB on your keyboard.
In the upper-left of the screen, close your second Virtual Desktop by clicking the X (Close) button in the preview tile.

NOTE: Any windows which you do not close (e.g. Task Manager) in a Virtual Desktop will migrate to the currently active desktop.
You will still need to close Task Manager if you no longer need the app running.


STEP 6:
Now that the ESO client has been closed, you will be able to click any app tile, or in an empty space on your desktop to bring it back into focus.
You may now launch the game again!