It sounds like you’re looking for intrusion detection or prevention rather than antivirus.
Great list here https://github.com/sbilly/awesome-security#ids--ips--host-ids--host-ips
However it’s likely that these do not run on asuswrt-merlin out of the box and may require additional setup or hardware.
You may even be good enough by using the built in firewall on the router interface and making sure no ports are open/forwarded.
Play store, profile picture, settings, network settings, auto update apps.
There are options for auto update over wifi only, or over data,