Second, do 300 people clap their hands and practice chanting Buddha on the playground, which violates the regulations on public security management? Is it an illegal assembly?

See if these people have some purpose to express their demands. If not, just gathering together to engage in activities will not affect public security and traffic, and it is not illegal.

Supplement: If you can't pass the examination and approval, there is no way out. So many people engage in collective activities, especially those with religious overtones, government agencies will worry about uncontrollable situations or emergencies.