You'd have a proof problem anyway -- how can you prove you got COVID from attending an event?
You need a good-faith basis for filing a claim. Even if you go to a full indoor gathering without masks and a lot of folks who went turn up with COVID, that doesn't mean that YOU got COVID from attending THAT event, especially if it's widespread in your community anyway.
While the waiver's probably no good, I'm not sure you can prove it, either. You might be able to intimidate some people into not suing, but that's not going to stop any decent lawyer from filing a class action suit on behalf of a bunch of sick attendees.
What a freaking mess.