Some fastgltf updates I needed to implement from their gl_viewer example:

[wark77]

in the load_image function https://vkguide.dev/docs/new_chapter_5/gltf_textures/:

[&](fastgltf::sources::BufferView& view) {
					auto& bufferView = asset.bufferViews[view.bufferViewIndex];
					auto& buffer = asset.buffers[bufferView.bufferIndex];

					std::visit(fastgltf::visitor { 
								   [](auto& arg) {},
								   [&](fastgltf::sources::Array& vector) {  //fastgltf::sources::**Array**& vector replaces fastgltf::sources::**Vector**& vector

									   unsigned char* data = stbi_load_from_memory(reinterpret_cast<const stbi_uc*>(vector.bytes.data() + bufferView.byteOffset),
					                                            static_cast<int>(bufferView.byteLength), &width, &height, &nrChannels, 4);

and in the gltf loading loop through meshes and primitives https://vkguide.dev/docs/new_chapter_5/gltf_nodes/:

// load vertex positions  vkguide.dev version

        {
            fastgltf::Accessor& posAccessor = gltf.accessors[p.findAttribute("POSITION")->second];  
            vertices.resize(vertices.size() + posAccessor.count);

            fastgltf::iterateAccessorWithIndex<glm::vec3>(gltf, posAccessor,
                [&](glm::vec3 v, size_t index) {
                    Vertex newvtx;
                    newvtx.position = v;
                    newvtx.normal = { 1, 0, 0 };
                    newvtx.color = glm::vec4 { 1.f };
                    newvtx.uv_x = 0;
                    newvtx.uv_y = 0;
                    vertices[initial_vtx + index] = newvtx;
                });
        }

//all accessors using ->second had to be replaced not just position, but all in the same way

auto* positionIt = p.findAttribute("POSITION");
auto& posAccessor = asset.accessors[positionIt->accessorIndex];  //can't use ->second anymore, changed to accessorIndex
vertices.resize(vertices.size() + posAccessor.count);                              

fastgltf::iterateAccessorWithIndex<fastgltf::math::fvec3>(asset, posAccessor,
[&](fastgltf::math::fvec3 v, std::size_t index) {          // had to change the glm::vec3 to fastgltf::math::fvec3 here

	Vertex newvtx;
	newvtx.pos = glm::vec3{v.x(),v.y(),v.z()};
	newvtx.normal = { 1, 0, 0 };
	newvtx.color = glm::vec3 { 1.f };//temp
	newvtx.uv_x = 0;
	newvtx.uv_y = 0;
	vertices[initial_vtx + index] = newvtx;
});

thanks for making this great guide! it really helps with breaking into understanding vulkan.