Thanks everyone. I found the answer to my question here:
https://foxnetlab.com/index.php/16-reviews/92-the-new-wireless-flagship-device-or-asus-rt-ac68u
To resume: Yes, 80 Celcius IS NORMAL. The RT-AC68-U is designed to support that:
Chip temperatures of up to 120°С are considered regular...
Until today, I used a script called by a cron on my Linux computer, to notify my DNS based filtering service of my current public IP address. (I use cleanbrowsing.org)
However, my computer is not always on.
So I want to move this notification to my router (rt-ac68u with the latest Merlin...