You don’t seem to understand the difference between mRNA vaccines and an immune escape mutation of a virus evading the immune systems response of the hosts.
Also part of why those beneficial mutations occurred is that a large (enough) portion of people weren’t vaccinated. The “potential” hosts, that required adaptation because they’ve seen how the virus looks like through vaccines, create an evolutionary pressure.
Even though this is about bacteria, not viruses and happens inside a petri dish, not in a natural environment, it quite illustratively shows how mutations work. Note, that even though the antibiotics are completely ineffective against the bacteria at the end, this does NOT mean, that it’s useless to begin with. It’s very effective, in fact so much that only small doses suffice to keep the bacteria away. But they mutate randomly yet with a selective (evolutionary) pressure. Maybe you’re too much of a “skeptic” to change your mind. But if you’re truly skeptic, try to be skeptic about your currently held believes too. The video: www.youtube.com/watch?v=plVk4NVIUh8