Under which circumstance would an officer NOT be exempt from firearm possession laws?

The reason "engaging in illegal activities" is the circumstance under which an officer would not be exempt from firearm possession laws is that possessing or using a firearm during illegal activities violates the law regardless of one's status as a law enforcement officer. Legal exemptions typically apply when an officer is performing official duties, acting in self-defense, or participating in training exercises where firearm use is sanctioned and monitored. When an officer engages in illegal activities, they lose their entitlement to the protections and exemptions provided by their position, as the law applies equally to all individuals in the context of illegal conduct. This maintains accountability and ensures that law enforcement officers uphold the law they are sworn to enforce.