Our galaxy supermassive blackhole, Sag A*, is only 4 million solar masses. The Milky Way has over 100 billion stars with a lot of them, many more times massive than our Sun. in fact the Milky Way is estimated at over 1.5 trillion solar masses. Did Sag A* eat a galaxy? No.
So, how about the most massive black hole, TON 618? That is 66 billion solar masses. That does put it in range of the smaller galactic masses. However, there is the problem of velocity. Things are not just floating around in space. Actually, everything has massive velocity. in one sort of orbit or another. The sort of orbit for galaxies, is a complex spiral, around all the galaxies around it. So, just imagine what this means. We can measure the proper velocity of the Milky Way, against the Cosmic Microwave Background. We are moving at 1.3 million miles per hour across the CMB. At these velocities black holes cannot eat everything, but they will gulp the part they are exposed to.. This means, the answer is no, black holes don’t swallow galaxies. Then how do they get so big?
They are part of the formation of some types of galaxies, as they undergo collisions with each other. They represent the core stars and dust collapsing, and merging, as another galaxy passes through it. Then, those galaxies collide. That can result in much more consumption of stars, and even the merger of the core black holes, over millions of years, of course.