Part of the Furniture
That's too much work, re-pasting things. and now that my wifi-6 client count is sufficient, I may just take advantage of the BestBuy deal you mentioned on the AX86 if good ol' AC86 is on it's way out (the JFFS creep issue has caused reboots 2 days in a row now...potentially a sign to move on)The thermal pads inside your router are leaking. This is very high temperature next to an open window with 12C air coming in. If you open your router you'll see large oily stains around thermal pads. This worsens the thermal transfer capabilities of the material. Happens after around 2 years use on this model. Every single one I opened had this issue (10 routers) in different stages.
Another evidence of the above - a new RT-AC86U holds around 74C in 26C room with little air circulation.
Count two. Your observations are perhaps unrelated to temperature and the reasons this CPU operates at close to 80C (with thermal protection threshold 100C) is barely enough size heatsink with minimum machining (resulting in large gaps) and inferior quality material thermal pads used. Both cost cutting measures. Replacing the pads with better quality ones drops the temperature with 10C. Closing the gap and use of good quality thermal paste drops the temperature with 20C. It's the same passive cooling method, but better made. Asus just saved $1 (or less) in manufacturing cost.
This router can't operate at 0-40C ambient temperature. It will overheat at 40C guaranteed. Yours will overheat at lower temperature.