Low GPU/CPU Usage

The i9-9900K can’t compete with the RTX3090.
CPU impact op FPS with RTX3090 (i9-9900K -2.5 FPS > Intel Core i9-12900K +6.2 FPS).

You can lower the settings that make heavy use of the CPU and set graphics as high as possible. Also look out with live and ground traffic and live wheather settings they are also heavy CPU users.