When thousands gather, the system sees opportunity.
https://untraceabledigitaldissident.com/how-to-communicate-securely-in-crowded-monitored-events/
Discussion
SimpleX Chat might have been worth mentioning instead of Signal especially for this use case.
And I'm so glad to see you didn't suggest Bitchat with their hard requirement for enabled Location Services!
You can just not be at these events to keep yourself private, and maneuver yourself out of these things.
If this is necessary, this is also a good guide.