The good news is that newer variants on Covid-19 will tend to be less virulent. A virus that kills its host, or disables so much that they take to their beds is a bad virus (as in "bad at being a virus", or "not good at it's job"), the death or voluntary isolation stops the virus spreading. Thus only relatively benign viruses have the wherewithal to be truly "successful" viruses. Evolution breeds excessive virulence out of viruses.
Like myxamotisis?
Understand the trajectory of myxamatosis https://www.nytimes.com/2022/06/20/science/myxoma-virus-rabbits-covid.html
You're asking for a long, long dad joke that starts "A rabbit went into a bar...".
Not
all viruses get less harmful over time
as they mutate, but most do. For any infectious disease (or parasitic disease) to kill its host
and survive itself it must either be (1)
both highly virulent and highly infectious, or (2) take a long time to kill its host (e.g. rabies, syphilis), or (3) have a complex lifecycle involving multiple hosts, some of which it is harmless to (e.g. malaria), or (4) be capable of surviving for a long time without a host (e.g. sporulating infections like anthrax).
Selection pressure in most cases selects for less virulent and more infectious organisms. Simple probability says that
random mutations that affect one aspect of harm (infectiousness, virulence, target species, complex life cycle, and so on) are more likely than random mutations that simultaneously affect two or more aspects. Simple probability also does not exclude this happening, just makes it less
likely.