The Asus router you pick seem to do some deep-inspection of trafic on the IoT devices you configured.
As IoT devices are (still) less secured, it is a good intermediate way to be safe.
I’m still convinced the IoT devices should be separated, but unfortunately, unless to take the time to get the skills, you’ll have to rely on the router and keep you firmware up to date.
edit: This thread also speaks about what’s needed between networks. it is something you may want to try.
Enjoy !
Tim