Ryzen 5900X strange CPU Usage, low FPS

Wow, that’s quite a big gap to me ^^

So the question is, how to find out where the problem is.
I reset my bios yesterday, no changes at all.
Any idea where to start?

What I found out by coincidence with a friend (he has an 5800X):
He got less FPS outside the cockpit (because of his GPU Limit, as he has a slower GPU), BUT he got more FPS in the cockpit.

To get numbers:
EDDM, Boeing T-45, clear skies

Cockpit me: 36 FPS (CPU Load: 18%, GPU Load: 62%)
grafik

Outside me: 51 FPS (CPU Load: 24%, GPU Load: 83%)
grafik

Cockpit friend: ~39 FPS
Outside friend: ~39 FPS

So what is kind of strange, that also the CPU Load is less in the case with less FPS. That lead me to think about, that something other than the CPU is throtteling?
Because it makes sense, that with fewer CPU Load I get less FPS, right?

So I’ve that behaviour with nearly every aircaft (btw Cockpit Refresh rate is set to low), that I get 15 to 20 FPS less in the Cockpit than in the outside view. BTW: If I look down in the cockpit to the instruments, I get more FPS, the low FPS I just get when looking threw the window.