So if the new R5 & R6 overheat after around 20-30 minutes of video...

...will they overheat after 30 minutes of constant viewfinder of rear screen use? The CCD is still live in both instances, the only reason I can see that it wouldn't would be if video does something different with the sensor.

I am not aware of many use cases that would have the camera 100% active over 30+ minutes so it might not be a real world issue, but still curious.

Storing data also generates heat. Live View data alone, or just looking thru EVF stores no data.

Ah, that makes sense.

There's also more processing going on, to compute the video frames to store, when actually recording. Today's electronics for mobile applications frequently have the ability to segment themselves, and hibernate segments not required for the task at hand. So instead of a CPU running idle cycles, it simply goes to sleep.