Can Two Stars of One Same Type Orbit Each Other?
Certainly, the figure only uses different masses because that's the more general possibility (after all, the two masses won't be exactly the same).  In fact, if you look at the distribution over mass ratio q in binary systems in Figure 1b in https://arxiv.org/pdf/1304.3123.pdf, it seems that the cumulative number of binaries with mass ratio less than q is more or less equal to q (where q is smaller mass over larger mass).  That means the probability of mass ratio between any q and q+dq is about equal to dq and nearly independent of q.  So the chance of the mass ratio being between 0.9 and 1 is about the same as being between 0 and 0.1, for example.  In some sense, that's like saying all q are equally likely.  And of course if q is near 1, then the stars will have the same age and be in the same evolutionary state, so will be the same stellar type as well.