Simcity 5 not using CPU and GPU, while having bad performance

Simcity 5 ins't using my PC components properly.

I'm getting a pretty bad frametime, with low CPU and GPU usages. I'm using a i7-13700k and RTX 4090.

Simcity was recently installed and this problem is happening since I started the game. No clue how to fix it.

Msi afterburner screenshot is attached.

P.s. in new saves, this problem does not seem to occur. It happens with old multiplayer saves with big cities.