There seems to be a little know, but crippling bug that is happening on Intel Based Mac's ever since the update to Big Sur. The issue is related to a single task callef kernel_task taking 500% or more of your CPU power when you plug in an external USBC connection, for instance a monitor or even the standard charging cable. So far Apple have not acknowledged it, but there are discussions on forums. No fixes have been made in all the updates to Big Sur.

I wondered, is this a common problem?

Here are more descriptions of the issue:

https://www.caldigit.com/my-intel-based-mac-crashes-when-un-docking-or-re-docking/.

https://www.macrumors.com/2021/02/03/macos-big-sur-external-display-issues/

https://developer.apple.com/forums/thread/678644