Since it is just the launcher and not the actual game executable file, bring up task manager and kill that process.
The launcher is needed to update the game. But you can run the game from the ESO64.exe file located in the "game/client" folder
If you make a short to the ESO64.exe file you can use that short cut to launch the game.
The game also randomly resizes any active Windows Explorer windows to be comically small. Weirdly, killing the process by task manager also resizes my Windows menu to be miniature; right-clicking and killing along the taskbar doesn't cause the bug.
For what it's worth, Windows just updated before this bug first appeared, so perhaps it's something to do with that.
Glad you got it fixed. My guess is the resolution set for the game is not the same the PC has set for the monitor which is why things are getting resized. Just a guess.