Third button has been "hidden" below the mouse wheel for well more than those 10 years, just press the wheel down and you'll hear a mouse button click.

You'll be surprised to know that there are still some mice that don't support that. Admittedly, I've only had that happen once in the last 15 yrs in a budget "gamer" mouse I instantly returned and replaced with a Logitech g903 at the time (though I've switched mice twice since, and both supported it)

And most Linuxes have option for dual click (right and left mouse button) to simulate middle mouse button.

Useful, as the wheel button is usually first to die in cheap mice.

Not useful, because it made it impossible to play Death Stranding on Linux :(

Ironically, Microsoft pioneered the scroll wheel.