[emmelaich]

The presence of the buttons doesn't matter much does it? Assuming a tap works as mouse click.

Maybe they're there for nipple users - it has one. Use fingers on the nipple and thumb on the button.

So to speak.

[hedora]

The third button is usually for scrolling.

[Beltalowda]

Or opening links in new tab, and paste if you use X11/Wayland.

[numpad0]

And for closing tabs/opening links in background. Both are required.

[ccouzens]

Maybe pressing both together registers as a the third button?