So EVERYWHERE I look up both “Crash in runnable thread background worker” and “failed to set completion port for job object “UE.ShaderCompileWorker.JobGroup”: The parameter is incorrect.” What I find is people saying that it’s an issue with their project. My first suggestion would be to run a verification scan of your engine installation through the Epic launcher.
One person said they migrated all the useful assets to a fresh project and then they could cook and package.
Another person said it was because they were using virtual textures, after they got rid of those and deleted the lighting cook data the problem went away.
This is a pretty rare occurrence apparently. You are running on hardware above minimum required specifications, yes?