I happened to stumble upon the list of service workers registered in my system. My default browser is Edge and the list of service workers is in edge://serviceworker-internals. For Chrome it is in chrome://serviceworker-internals. I was surprised by all the websites with service workers in my system. I do not recognize very many of the websites and many are suspicious. At the top are service workers for extensions; I left them but I unregistered any others that I did not recognize or really do not need.
Does anyone know how much of a threat they can be? I found the article The Service Worker Hiding in Your Browser: The Next Web Attack Target? but I only glanced over it. For the moment I will simply continue weeding out the ones I do not want.