I run Linux Mint 18.3.....which is a derivative of Ubuntu
In the time I have run Linux, I have never encountered any malware/behaviour etc etc that has made me wish I had an AV installed
At one time, I did install clamav , and instantly regretted it. Poor performance, unstable/weird behaviour......I uninstalled Linux mint and started afresh with a clean install.....and have never regretted that decision.
I do realise that the first thing a windows user will look for is some form of protection....av etc etc
1. enable firewall
2.
Make your browser safe (malwearebytes have an addon which will protect you from adds/clickbait/malware/scams.......
HERE )
3. Practice safe browsing.
Enjoy your Linux/Ubuntu/whichever distro you happen to have......without the 'drag' of an av.
I cannot give an opinion about apparmour. Others may help here re its effectiveness/effect on system etc etc