After using Windows my hole life, i wanted to try a new operating system. I settled on Kubuntu since I liked the design and the easy usability of Ubuntu from a newbie perspective. While using it for browsing I haven't noticed any problems. However when I try to load some CPU intensive tasks I can feel a significant performance hit compared to windows. But first of all my configuration: I'm running a HP Probook 470 G5 with a Intel i7 8550u which should be capable of 1.8GHz on all cores and 3.7GHz burst. However when I load the CPU (e.g a stresstest) it will only run at 1.2GHz (output from i7z)

As you can also see in the picture the CPU isn't thermal throttling.
As soon as I reduce the load the clockspeeds return to "normal"

I also issued sudo cpupower frequency-set -g performance to change the CPU profile to performance. This didn't show any difference in clock speed under load.
Also note that I'm running all test with plugged in power cord. Furthermore no advanced power manager should be running, but you can prove me wrong ;) If you need any more information I will add them as soon as possible.
I assume it has something to do with the general power management of the system, but I can be wrong. Hopefully we can find a solution. Otherwise I will need to change back to windows ;(
The Kernel Version is 5.8.0-44-generic
Edit: I noticed that the temps spike (at least s-tui show that) on the CPU die itself, then the CPU throttles and never recovers.
Edit: Turning the CPU frequency down to 2GHz result in a way longer CPU burst, but only at 2 GHz. This may indicate that it's in fact a thermal issue. However I would consider 60°C as more than adequate cooling.