Where are BPMon alerts configured and activated, and why the operations branch specifically?

Alert objects are assigned by process/step/interface, stored in the alerting library, assigned directly in Solution Documentation.

All BPMon alerts are configured/activated in the operations branch because it's always identical to production (a child branch's change released to production also auto-releases into operations). Assign via right-click process step → New → Operations → Alerting, then set thresholds (yellow/red) + notifications in Object Administration (Fiori), then generate + activate.