mRNA not-vaccines can certainly be dangerous, and the covid one did a lot of harm and they lied about it. But its not gene therapy. mRNA is the transcribed DNA (now RNA) that goes to ribosomes to create proteins. Its one way. It can't change DNA.
But we do have gene therapy technology, and we can change the DNA of somatic cells. I just finished a very eye opening book called "A Crack in Creation" by Jennifer Doudna, who is the main inventor of CRISPR cas9.