Problems with static mesh and Nanites

Hi guys
Why after enabling Nanite support my mesh becomes gray and low poly?

Hello Michal_Ratajczak, welcome to the Unreal community.

Congratulations on utilizing Nanite!

There are a few points of troubleshooting I would look into:
RHI (in project settings): If it is not already, I would consider changing it to DX12.
The mesh may be displayed as a FallBack mesh. The Fallback Mesh is the generated mesh used when Nanite rendering is not supported.

Additional specifications can be found here in the documentation.

I hope the documentation helps.