1. Open your Steam Library
2. Right click the game's title and select Properties
3. On the General tab you'll find Launch Options section.
4. Enter the launch options you wish to apply and just add "-dx12" (without " ").
5. Close the game's Properties window and launch the game.

Note: your GPU needs to support dx12 (almost every gpu does support it)

Limit your framerate to 60 Fps! This will fix most of the game's bugs like beeing stuck in the stunt cam and sound bugs while driveing.

Biggest impact on performance:
-Car reflections: set to "screen"
This almost doubled my FPS.

Some smaller impacts:
-Visual effects: set from "Ultra" to "High" (almost no visual difference)
-Cloud quality: set to "Volumetric" (almost no visual difference)
-World shadow quality: set to "medium" (has a visual impact)
-Streetlight quality: set to "medium" (has a visual impact)
-Vehicle light quality : set to "medium" or "low" (has a visual impact)

You can also set all settings from "Ultra" to "High". This will have little to no impact on visual appearance but it will give you a more consistent framerate.