Sure, if you want to get into a semantic argument. The point is that the mechanism isn't complex, there is decades of research and multiple studies showing us it's likely safe, and still people are out here saying things like, "It's totally untested!"
Like, at some point we have to trust science and accept that studies and test groups will give us some reliable safety guesses. People generally have no idea how much research has already gone into this vaccine because they've been taken in by all the media coverage around the mRNA vaccines claiming the technology is new.
Let me try explaining via an analogy. It's like the folks who are really worried about 5G signals because they are new. On the one hand, yes, humankind has not had long term exposure to 5G signals. On the other hand science has a fairly complete understanding of various electromagnetic spectrums and is the phenomena of using electromagnetic phenomena is hardly new.
So yes, mRNA vaccines are 'new', but only in the way 5G is 'new'. We may not have deployed it widely before, but we're pretty dang sure we understand it.