Persona (2000)

Into the bully-infested home room class struts a fearless, ceramic-masked student. Squarely confronting a gang of ruffians, it is soon discovered that behind the mask is none other than Danta, an otherwise weakling student who has heretofore been picked on relentlessly by these same bullies. Donned with his mask, however, Danta exhibits a totally other personality, lacking fear and intimidation. The other students, looking on, soon experiment with the power of masks and find to their glee that behind a facade of anonymity, they experience an overwhelming power to act without the confines of self-consciousness.

Unfortunately the movie Persona is not yet available on HBO Max.