See https://github.com/flutter/engine/blob/main/shell/platform/embedder/embedder.cc#L565 and how things are passed down to glfwGetInstanceProcAddr at https://github.com/flutter/engine/blob/main/examples/vulkan_glfw/src/main.cc#L394

This does make me wonder whether the Vulkan GLFW example ever worked at all?