Wrong but you go with that.
Las Vegas -- armed band members who hid in fear in their camper
Uvalde -- armed school officer
Kirkwood City Hall massacre -- 2007, armed police officers
Sante Fe, TX -- armed school officers
Marshall County High School, KY -- ditto
Marjory Stoneman Douglas High School, FL -- ditto
Great Mills High School, MD -- ditto
Buffalo NY grocery store -- armed security officer (killed by shooter)
Pulse Nightclub, FL -- armed security officer (sued by victims' families for failure to act)
The 'Good Guys With Guns' Keep Failing to Stop Mass Shootings
As I said, if a good guy with a gun actually gets the shooter, it's pretty rare.