Sketch – Arc Shape?

You could fake it by using the Layer > Vector > Rotate Copies. Simply choose a rectangle shape and then create any number of copies. The more copies you create, the smoother the arc will be.

You can also create Two Circles, subtract them, and then subtract a rectangle in half:

Finally, you could draw it with the pen tool (though you’d lose some accuracy in the process.

Unfortunately, you won’t be able to adjust the angle or the sweep. But if you manipulate shapes on top of shapes and use the Pathfinder or Transform tools, you should be able to achieve your desired effect.