My guess, and this is just completely a guess, is that you are bottlenecked at the CPU. Sure it may only be at 50% but the game is probably only using 2 cores and maxing those at 100% each, making overall CPU 50%.

Is it 50% on all cores or 100% on half?

Does this happens in other games or just rust ?

Besides Rust I play CS GO which isn't demanding so it runs at 200-300 FPS while GPU and CPU are working at around 50%.

So if even playing CSGO your GPU usage stays at 50%, then it's more likely a driver issue. Try reinstalling the NVIDIA drivers.

Its not pinned at 50% its around 50% (40-60%). I think it happens in CS GO because game graphics are at highest and PC isn't supposed to make more than 300 frames...

Where can I check that? I guess it is 50% on all cores cuz temps are nearly same and clock speed too...

CS GO doesn't have a frame cap, as far as i know, so as long as your gpu and cpu can take it, they should increase FPS.

If you're having this issue in every game you play, then it's most certainly a GPU driver issue or it's a defect GPU.

I was using debloated driver so I reinstalled my drivers and its pretty much same... GPU still working at around 50%

Task manager, where did you check your CPU usage to begin with?