first off, i have 2 dead friends from covid. diagnosed. dead. aggregated, millions around the planet. began before the vaccines existed.
you have a handful of kids who got myocarditis that went away in weeks. you then have speculation maybe something happens in the future.
the vaccines have at this point been through billions of arms and nothing happened. that is far more safety testing than most drugs ever get.
on how the "vaccine mutates," this is really not complicated. they don't give the same exact vaccine over and over. they try to anticipate what the most prevalent and roughest variant will be, then make the vaccine for that, for the season. they already did that for flu. there are many flus. you guess which one is going to be the issue. you hope it doesn't evolve or you guess wrong.
one of the running concerns on covid was would it evolve (a) out of immunity and/or (b) out of the vaccine response. over time it will evolve out of the vaccine response.
in bigger terms, they were already developing the basic structure of mrna vaccines before covid, for use for many things. they basically pop in a chunk to trigger that specific virus/variant. they are also developing mrna for other viruses/cancers.