I have tried yo unwrap this mesh,

but How to make seams? Have tried several variants, but result is always this

Is the texture you are planning to use round like the mesh? If it is, I would simply unwrap using the “Project from View”, and make sure your view is facing the mesh.

it’s a normals issue. in the 3D window, in edit mode, select all and hit ctrl N ( recalculate normals outside )