Override C++ event in Blueprint

have you tried adding “_Implementation” to the function name in the .CPP?:

#.h

 UFUNCTION(BlueprintNativeEvent)
 void OnBeginFocus();

#.cpp

void AUsableActor::OnBeginFocus_Implementation()
 {
     // Used by custom PostProcess to render outlines
     MeshComp->SetRenderCustomDepth(true);
 }