was based on "outside" events like the July 4th super-spreader at an annual festival in Provincetown, MA. - https://www.democraticunderground.com/10142777706
The problem with trying to do a "study" in a formal sense is that you end up purposely infecting people (and if you use a blind method, then participants wouldn't know if they are or not). And then you'd have to have control groups and what not, and that is just not going to happen.
So what they do is use the "real world" data collected by Health Departments to piece together what happened, interview the impacted, and then compile the data collected for what was observed over some "x" period of time, etc., and publish it.
The "early release" paper was here - https://www.cdc.gov/mmwr/volumes/70/wr/mm7031e2.htm?s_cidmm7031e2_w
The final paper was here - https://www.cdc.gov/mmwr/volumes/70/wr/mm7031e2.htm
Lollapalooza wasn't a "super-spreader" per se but it also wasn't a "no spreader at all". They supposedly had quite a bit of mitigation protocols put in place including pretty much requiring vaccination (they estimate 90% were) and/or a negative COVID-19 test before entry. There were 203 cases reported. One of the problems that many Health Departments have had too is contact tracing and it's possible there were more cases there but they haven't been able to trace them and/or people may have refused to admit to being there.
Last year there were indications that the BLM protests weren't super-spreaders either - but I think that may have been because many participants were masked and probably more importantly, they were continually "moving " (marching).