There do exist "noroot" Android firewalls; I am not sure how they work (I think by somehow becoming interfaces - like "noroot" packet sniffers), but very probably not through `iptables`.
There are products on GitHub; I am looking at NetGuard (from, I think, Marcel Bokhorst aka M66B - the project has many forks). The .md says, «The only way to build a no-root firewall on Android is to use the Android VPN service».