Kernel task takes about 500% CPU after connecting external monitor I work with macBook Pro (15 Inch 2019, Catalina OS). I can't work with external monitor. 3-5 minutes after pluging in I have kernel_task that takes something about 500-900% CPU. I know there are some similar topics - the main suspect is overheating in such case. I have some changes in temperature, but it's hard to say for me if temperatures are still in ok spot. I have highlighted the biggest changes.
I would suggest moving your charging plug from the left side of the MacBook Pro to the right side. Similarly you can experiment with plugging in the monitor on the other side.
The two sides have different reactions in terms of temperature, so on one side it might not make much difference - and on the other side it could be just above the threshold that triggers an attempt to lower the temperature by making kernel_task occupy the CPU (in idle mode) to save power.