Hi, same problem here, i have:
I5 9600K
32gb ram
Rtx 2060 Super 8Gb
Tested in LIML (payware airport) 15-25 fps A310, B737 Pmdg 40\50 Fps, Fenix A320 30\40
With A310 Cpu and Gpu seems are sleeping, 35\40% cpu use and 20\25 Fps Gpu with low gpu clock, 1200\1500 mhz and not 1900 max
1080P change from low to ultra hight setting, change 2\3 fps only, i try both dx11 and 12 and dlss yes and not.
I hope can help you to investigate.