It does not work
It doesn't work. The instance is created, i have the ip address, I put it in the browser, i have not firewall settings blocking it. Nothing.
Thanks OhiraKyou as noob to AWS this is what I was missing.
For anyone visiting this later, you must add a security group to the instance with an inbound rule for HTTP (and, optionally, HTTPS). The rest of the settings (protocol, port, and source) should be automatically filled in when you select the type. For reference, the resulting sources shown on the inbound tab after adding the rule should be 0.0.0.0/0 and ::/0. After applying the security group to the instance, reboot the instance and wait a while. You should then, eventually, be able to reach the Mautic login screen from the instance's public IP.