Requiring masks for singers outdoors on a stage is really nuts. Aerosole science is clear that there is zero infection risk in that scenario.
Walmart‘s decision to drop mask mandate for all customers is dangerous in contrast. Another example of how irrational society as a whole deals with the virus.
[Added:] If courts take account of science, no visitor would be able to successfully sue an event organizer claiming he/she was infected by someone from an outdoor stage.