Mutations are happening in both populations. Specific mutation that make the vaccine ineffective are happening in vaccinated people.
This vaccine doesn't prevent covid the way the smallpox vaccine does. This is a new type of vaccine trying to reduce deaths. Calling the same is a marketing trick.
Though I'm also curious why this only happens for this virus, and not any of the others we've destroyed with vaccination like smallpox, or reduced to nothingness like polio or measles. (short version: you don't know what you're talking about).