It might be related to the connection used. I've heard that the issue doesn't present when using DisplayPort as opposed to HDMI, but I have tried different dongles.
And it's not terribly bad, just that I pretty much draw the full 92W the power adaptor supplies and get the mentioned thermal throttling much sooner than without.
Running a bunch of docker containers, slack, and general everyday workflow. Doing all the good stuff like ad-blocker and checking process monitor.
Our solution isn't the most lightweight, but still the end result is that plugging in an external monitor (1080), my productivity goes down dramatically which is the opposite of how multiple monitor setups are supposed to work. :-)