One small point that nobody considers is that the COVID collection of SARS-2 viruses are living organisms and like all other living organisms must possess sexual reproduction which in bacteria and upwards in the phylo-genetic chain is termed meiosis as apposed to non-sexual reproduction or mitosis. This involves a sharing of genetic information which may account (in addition to mutation) for the rapid evolution of new COVID variants!
Human intervention is what leads to variants seen so far. Monoclonal treatments used to treat human petri dishes has led to most variants. 2 have been observed happening my in real time. Think RNA silencing. Mutations and variants are the process of defence. RNA comnicates with the nucleus to rewrite to defend and evade.