Not disagreeing with you at all: that physics fact always come up. My honest question is: if it's a perfect thermos, what does, for example, the ISS do with the heat generated by computers and humans burning calories? The ISS is equipped with a mechanism to radiate excess heat into space? Or is the ISS slowly heating up but it's not a problem?

Massive radiators. In this photo[0], all of the light gray panels are thermal radiators. Note how they are nearly as large as the solar panels, which gives you an idea about the scale needed to radiate away 3-12 people's worth of heat (~1200 watts) + the heat generated by equipment.

[0] https://images-assets.nasa.gov/image/jsc2021e064215_alt/jsc2...

Let me google that for you.

https://en.wikipedia.org/wiki/External_Active_Thermal_Contro...

The ISS has giant heat sinks[1]. Those heat sinks are necessary for just the modest heat generated on the ISS, and should give an idea of what a sattelite full of GPU's might require...

[1] https://en.wikipedia.org/wiki/External_Active_Thermal_Contro...

The ISS has MASSIVE radiators. Most of its volume is radiator. 900 cubic meters of space 2500 square meters of radiator.

The TL;DR is they radiate it into space via large, high surface area arms that stick out of the station.