The vaccine cuts down on contracting and spreading covid, and it also causes the virus to replicate less as the body will destroy it faster (somewhere around 2 days in the rare case of a breakthrough infection versus a week in the unvaccinated). Viruses don’t mutate due to pressures. They mutate on a fairly stable schedule given the reproductive method.
Those mutations are then either beneficial or not. An example of a mutation that is not beneficial: Down’s syndrome, which you may have based on your complete lack of understanding given an internet connection. An example of a beneficial mutation is sickle-cell, which makes the person who has it less likely to suffer diseases found in Africa, which is why black people have that mutation. The same is true of mutations that allowed people to drink milk. It is thought that Europe went through a period where this was beneficial, so all those who had the mutation survived, causing Europeans to be much less likely to have lactose intolerance.
Currently the delta variant, which was first detected in India prior to vaccination being widespread there, was a mutation that occurred, as stated above, due to massive replication, and it out competed other viruses due to its ability to replicate extremely quickly, causing it to be more transmissible.
Viruses do not think “wouldn’t it be great if I could do (insert thing)” and then replicate a virus that can do that anymore than you can wish your child to be smart. You just don’t have the genes to do that. Your child will be what your child is, and whether your child is able to reproduce will determine whether your genes go to the next generation after that child.