Could mRNA Covid vaccines be dangerous in the long term?

So, they use mRNA as code that cellular machinery will use to produce the spikey protein of the corona virus.

Why not just use yeast or something to produce the protein outside the body and inject the protein instead?

I believe current vaccines are already dangerous in the long run. A lot of autoimmune diseases are caused by vaccines. Antibodies mutate and not always in your favor. I'm certain that mRNA vaccines will be even more dangerous because they introduce more layers where things can go wrong.

Viruses have been around for a long time. Coronaviruses predate humans or hominids. They're as old as mammals. Biology has had hundreds of millions of years to figure it out. If there was an easy solution (like produce more Vitamin D or create an antigen), it would have done so. The only reason it hasn't is because the solution is worse than the problem.