Insofar as attention is zero sum, making circus arts mandatory would not make those that are at risk of commiting violence more able to get attention. For that to work, you would have to encourage the relatively violent-prone to learn circus arts and discourage the relatively non-violent-prone.

I don't think the kind of attention those people need is about being on stage. Human to human connection is likely more valuable.

I know several teachers of circus arts in schools. It replaces sport classes. Helps teach balance, confidence, hobbies, skills, and fun.

Just ask the offending schools if they will consider it; or ask a circus teacher if they will approach the offending school.

offending == school that has taken your fancy to try to improve.

Less ambitious, but music and art were required at my school. Not much, just one performance to the class and one public piece were required. I don't know how to check if mass shooters were deprived of other forms of public expression.