I have one of these cases[1] for my Pi4 4GB from Amazon. Comes with heatsink and small fan (very quiet). Right now running "watch -n 1 vcgencmd measure_temp" puts it at 36C idle. Well I guess it is actually running k3s with no deployments/pods, so fairly idle.

I do remember it running a bit hotter before I updated to the latest firmware via "sudo apt full-upgrade" a few days ago.

Running "stress -c 4" gets it up to about 50C ...

[1] https://www.amazon.com/Raspberry-iUniker-Heatsink-Model-Sing...