Can Laptop Cooler or AV Cooler Degrade WiFi Signal??

In the vast majority of cases, a router doesn't need additional cooling in in the specified environmental conditions.
Products like these will pretty much all go through a hot box test where they will place the product into a temperature controlled chamber with no active airflow, and run the product at full load at various temperatures.

This is why you will typically see specs like Operating temperature: 0° to 40°C (32º to 104ºF)
90% maximum relative humidity, noncondensing.

The main things that can negatively impact the ratings are if the device is exposed to direct sunlight where the casing can experience like when a car is parked outside on a sunny day. Other impacts can be if the product is mounted or placed in a position or angle in which the passive cooling was not designed for, or if placed on a surface that restricts natural convection for some of the vents, e.g., a router placed on a carpeted floor where the feel of ht product sinks into the carpet a little, and blocking off some of the bottom vents.

While it is hard to get datasheets for newer SOCs and radios, for many older 802.11ac items, it is not uncommon to see them have operating temperature ratings of -40°C to 100°C along with thermal protections where they should do a thermal shutdown, where the overheating part should shutoff until they get powercycled.While just like any device, it is not good for them to run at their max temperature 24/7, they should be fully stable within their temperature ratings.