Well, maybe. Last I heard, the evidence on omicron’s severity is uncertain: A smaller proportion of those infected with omicron are dying, but it’s unknown how much of that is due to vaccines and better care.
And yes, there’s a tendency for pathogens to evolve to be less deadly, because a dead host won’t spread the pathogen. But covid, of any strain, already has a low enough lethality that any selective pressure to become even less lethal would be extremely weak.