Voxel terrain generation performance problems

I am trying to create a minecraft clone to practice some stuff in Unity including Raycasting, terrain generation and player controlls.

Terrain is generating without any problem with a perlinNoise.

My problem is the then following performance problems.

The terrain is only 1 block high with no underlying blocks. Each block constist out of 6 planes with a 64x64 texture. I generate terrain at 200 x 200 size.

I can't imagine why 4000 voxels with such simple textures can lag out whilst my pc runs objects with 50k tris and complex textures without any problem.

My code:

    [...]

   

    public int xVoxels = 200;

    public int zVoxels = 200;

   

    [...]

   

    for (int x = 0; x < xVoxels; x++){

        for (int z = 0; z < zVoxels; z++){

   

            // voxel = script parameter

            GameObject newVoxel = GameObject.Instantiate(voxel);

            Vector3 position = new Vector3();

           

            position.x = xVoxels/2 + x;

            position.z = zVoxels/2 + z;

            // PerlinNoise stripped out for testing

            position.y = 0f;

   

            newVoxel.transform.position = position;

        }

    }

Solutions I tried:

Combining meshes

Combining all meshes to a single one per material worked wonderfully... until I wanted to interact with each voxel determined by Raycasting from the Camera, I had a raycast hit to the combined mesh and not to my determined voxel

Generating the planes myself

Instead of using the unity plane object I generated all vertecies myself, same performance problems

 

Look around at https://0fps.net/2012/06/30/meshing-in-a-minecraft-game/
You can also look at https://old.reddit.com/r/VoxelGameDev/ for more references (in the sidebar, and their discord @ https://discord.gg/0pO6Iw0eVUKYrJPv )