I tried the game on a Windows laptop without any problem, it's something related to the right click gesture on a Mac? Keep in mind you could always press "F" to flag a cell :)
I didn't realize you could use "F", thanks! and yes, the difficulty is that Mac laptops don't have physical left mouse and right mouse buttons, so the only way to right click is either to ctrl + click (which the game doesn't recognize as a right click) or or to click the trackpad with two fingers, which makes it very easy to accidentally left-click when trying to right-click