3D viewer for iOS using MetalKit and Swift - Depth doesn’t work

I’m using Metal with Swift to build a 3D viewer for iOS and I have some issues to make the depth working. From now, I can draw and render a single shape correctly in 3D (like a simple square plane (4 triangles (2 for each face)) or a tetrahedron (4 triangles)). However, when I try to draw 2 shapes together, the depth between these two shapes doesn’t work. For example, a plane is placed at Z axes = 0 behind a tetra which is placed at Z > 0. If I look a this scene from the back (camera placed somewhere at Z < 0), it’s ok. But when I look at this scene from the front (camera placed somewhere at Z > 0), it doesn’t work. The plane is drawn before the tetra even if it is placed behind the tetra.

I think that the plane is always drawn on the screen before the tetra (no matter the position of the camera) because the call of drawPrimitives for the plane is done before the call for the tetra. However, I was thinking that all the depth and stencil settings will deal with that properly. I don’t know if the depth isn’t working because depth texture, stencil state and so on are not correctly set or because each shape is drawn in a different call of drawPrimitives.
In other words, do I have to draw all shapes in the same call of drawPrimitives to make the depth working ? The idea of this multiple call to drawPrimitives is to deal with different kinds of primitive type for each shape (triangle or line or …).

This is how I set the depth stencil state and the depth texture and the render pipeline :

   init() {
   // some miscellaneous initialisation …
   // … 
   // all MTL stuff : 
   commandQueue = device.makeCommandQueue()
   // Stencil descriptor
   let depthStencilDescriptor = MTLDepthStencilDescriptor()
   depthStencilDescriptor.depthCompareFunction = .less
   depthStencilDescriptor.isDepthWriteEnabled = true
   depthStencilState = device.makeDepthStencilState(descriptor: depthStencilDescriptor)!
   
   // Library and pipeline descriptor & state
   let library = try! device.makeLibrary(source: shaders, options: nil)
   // Our vertex function name
   let vertexFunction = library.makeFunction(name: "basic_vertex_function")
   // Our fragment function name
   let fragmentFunction = library.makeFunction(name: "basic_fragment_function")
   // Create basic descriptor
   let renderPipelineDescriptor = MTLRenderPipelineDescriptor()
   // Attach the pixel format that si the same as the MetalView
   renderPipelineDescriptor.colorAttachments[0].pixelFormat = .bgra8Unorm
   renderPipelineDescriptor.depthAttachmentPixelFormat = .depth32Float_stencil8
   renderPipelineDescriptor.stencilAttachmentPixelFormat = .depth32Float_stencil8
    
    
    //renderPipelineDescriptor.stencilAttachmentPixelFormat = .stencil8
   // Attach the shader functions
   renderPipelineDescriptor.vertexFunction = vertexFunction
   renderPipelineDescriptor.fragmentFunction = fragmentFunction
    
   // Try to update the state of the renderPipeline
   do {
        renderPipelineState = try device.makeRenderPipelineState(descriptor: renderPipelineDescriptor)
   } catch {
        print(error.localizedDescription)
   }
    
   // Depth Texture 
   let desc = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: .stencil8, width: 576, height: 723, mipmapped: false)
   desc.storageMode = .private
   desc.usage = .pixelFormatView
   depthTexture = device.makeTexture(descriptor: desc)!
   // Uniforms buffer
   modelMatrix = Matrix4()
   modelMatrix.multiplyLeft(worldMatrix)
   
   uniformBuffer = device.makeBuffer( length: MemoryLayout<Float>.stride*16*2, options: [])
   let bufferPointer = uniformBuffer.contents()
   memcpy(bufferPointer, &modelMatrix.matrix.m, MemoryLayout<Float>.stride * 16)
   memcpy(bufferPointer + MemoryLayout<Float>.stride * 16, &projectionMatrix.matrix.m, MemoryLayout<Float>.stride * 16)
   }

And the draw function :

function draw(in view: MTKView) {
    // create render pass descriptor
    guard let drawable = view.currentDrawable,
          let renderPassDescriptor = view.currentRenderPassDescriptor else {
        return
    } 

    renderPassDescriptor.depthAttachment.texture = depthTexture
    renderPassDescriptor.depthAttachment.clearDepth = 1.0
    //renderPassDescriptor.depthAttachment.loadAction = .load
    renderPassDescriptor.depthAttachment.loadAction = .clear
    renderPassDescriptor.depthAttachment.storeAction = .store

    // Create a buffer from the commandQueue
    let commandBuffer = commandQueue.makeCommandBuffer()
    let commandEncoder = commandBuffer?.makeRenderCommandEncoder(descriptor: renderPassDescriptor)
    commandEncoder?.setRenderPipelineState(renderPipelineState)
    commandEncoder?.setFrontFacing(.counterClockwise)
    commandEncoder?.setCullMode(.back)
    commandEncoder?.setDepthStencilState(depthStencilState)
    
    // Draw all obj in objects
    // objects = array of Object; each object describing vertices and primitive type of a shape
    // objects[0] = Plane, objects[1] = Tetra
    for obj in objects {
        createVertexBuffers(device: view.device!, vertices: obj.vertices)          
        commandEncoder?.setVertexBuffer(vertexBuffer, offset: 0, index: 0)
        commandEncoder?.setVertexBuffer(uniformBuffer, offset: 0, index: 1)
       
        commandEncoder?.drawPrimitives(type: obj.primitive, vertexStart: 0, vertexCount: obj.vertices.count)
    }
    
    commandEncoder?.endEncoding()
    commandBuffer?.present(drawable)
    commandBuffer?.commit()
    

}

Does anyone has an idea of what is wrong or missing ? Any advice is welcome !

Edited 09/23/2022: Code updated