AT&T Note 9. You're right, Device Maintenance doesn't have Security tab. They want you to use their own, AT&T Mobile Security.
Considering prior unlicked Galaxy phones had a brand I won't touch. CM I think. Cheetah is another.
If I was to, I've had ESET for two years not really doing much except scan in background and tell me my browser isn't one it supports.
Norton is a performance killer, ling time Kaspersky Windows in the past and tried it on Android. Probably Malwarebytes but never really found anything other than what AT&T put in that got flagged. Same with BitDefender. Think better off being current as you can and use good practice with what you use and do.