My guess is that less infectious mutations occur, but we don’t hear about them because they do not spread.
The drug companies and health organizations worldwide are looking out for bad new mutations all the time. With the skills acquired in this century new vaccines will be produced when needed.
The best way to stop Covid is to vaccinate everyone, everywhere. Many countries have only a 2% vaccination rate, so we have a long way to go.
Paxiled did a really great job of explaining how and why a virus mutates. I'll just add a couple of tidbits for interest.
Viruses, unlike bacteria, require a living host in order to maintain activity, and to replicate, and to mutate. Once a virus is on a surface, it begins to lose the ability to infect. The rate at which this happens depends on the virus. For example, we know that cold and flu viruses can spread if we touch a surface that someone has sneezed on, and then touch our nose or mouth, and that the virus can maintain enough activity to infect for at least several days. With COVID, it does not appear that people are being infected via surfaces, meaning the virus loses activity at a very rapid rate once outside of a living host. This is good news, because you can imagine how much higher the infection rates would be if COVID were transmissible via surfaces.
Viruses also mutate at different rates. For example, the measles virus is extremely stable, and does not tend to mutate. That is why most people who either get measles, or are vaccinated against measles, are immune for life and do not need additional boosters. The common cold, the flu, and COVID mutate relatively rapidly, which is why we can get the cold and flu multiple times in our lives (probably COVID too), and why we need boosters for the flu and COVID vaccines.
The only way to prevent further mutations, or to slow the rate at which the virus mutates, is to prevent person-to-person transmission. COVID is showing a pattern of increasing, not decreasing, virulence, so there is no reason to think that it will settle into a milder form. Because it is impossible to predict when and how this virus will mutate, unfortunately, updated vaccines/boosters will be reactive rather than proactive - meaning we have to wait until the virus mutates until the vaccine can be updated.
Viruses mutate in the same way that every thing on Earth that has a survival instinct mutates. When it happens in plants and animals such as humans we call it adaptation, and theoretically at least adaptations occur randomly and those that work to increase survival chances stick around. Viruses are in an odd category; they're not really considered to be alive but they definitely have a survival instinct, so what we call it isn't really important. Mutations are random, and if they allow the virus to survive they stick around and can cause other mutations to go away as they are out-competed. The way you prevent mutations is to deprive the virus of a host, as they can't survive without one. Since it crossed into humans, we're the hosts, and for the virus in this adapted state needs susceptible humans in order to replicate and thus survive. How do you prevent it from doing that? Wear a mask that is strong enough to prevent you from becoming infected. At this point, that's probably only an N95 mask, not the cloth ones we've been using or surgical masks, because not enough people have worn them and this allowed the virus to expand unimpeded. Social distancing is the other technique that if at the beginning of this whole mess we had all done as instructed the virus would have been better controlled until the vaccine arrived or a therapeutic was invented that cured us of it. But although we have vaccines, they are not 100% effective, some are more effective than others, and not enough people have gotten them to reach herd immunity, which is when there are not enough host for the virus to continue to thrive and it goes dormant. Because of the politicalization of this virus and masking and vaccines by right wing movements all over the world people have intentionally allowed it to spread, as if to prove our liberty, but you can't really enjoy liberty if there's a pandemic running loose. So the answer is, get everyone vaccinated, which means not just where you happen to live but the entire world, and in the meantime wear a mask and social distance. Anything less and it will continue to mutate as it tries to survive. It is possible that over time the virus will mutate to a much less dangerous and lethal form so we'll stop fighting it and just live with it, which is what the common cold did. So while it won't become harmless most likely, it is possible. A lot of people will suffer and a lot will die in the meantime, though, so I wouldn't want to wait for that to happen as my strategy. The reason the delta variant got so contagious isn't known for certain, but it appears to have happened in India when they dropped mask and distancing mandates. India has a lot of people and a lot of them don't have strong immune systems, as there is a lot of poverty there. Just as in the US, we have a ton of sick people and obese people, and they make up a lot of who got covid the worst and allowed it to spread. There have been several variants so far, so we should expect more as long as we don't do what public health officials say to do, and we're not doing that.