/usr/include/mirplatform/mir/ is in libmirplatform-dev 0.31.1-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/mirplatform/mir/client/
/usr/include/mirplatform/mir/client/client_buffer.h
/usr/include/mirplatform/mir/client/client_buffer_factory.h
/usr/include/mirplatform/mir/client/client_context.h
/usr/include/mirplatform/mir/client/client_platform.h
/usr/include/mirplatform/mir/client/client_platform_factory.h
/usr/include/mirplatform/mir/client/egl_native_display_container.h
/usr/include/mirplatform/mir/client/egl_native_surface.h
/usr/include/mirplatform/mir/emergency_cleanup_registry.h
/usr/include/mirplatform/mir/graphics/
/usr/include/mirplatform/mir/graphics/atomic_frame.h
/usr/include/mirplatform/mir/graphics/buffer.h
/usr/include/mirplatform/mir/graphics/buffer_basic.h
/usr/include/mirplatform/mir/graphics/buffer_id.h
/usr/include/mirplatform/mir/graphics/buffer_ipc_message.h
/usr/include/mirplatform/mir/graphics/buffer_properties.h
/usr/include/mirplatform/mir/graphics/cursor.h
/usr/include/mirplatform/mir/graphics/cursor_image.h
/usr/include/mirplatform/mir/graphics/display.h
/usr/include/mirplatform/mir/graphics/display_buffer.h
/usr/include/mirplatform/mir/graphics/display_configuration.h
/usr/include/mirplatform/mir/graphics/display_configuration_policy.h
/usr/include/mirplatform/mir/graphics/display_report.h
/usr/include/mirplatform/mir/graphics/egl_error.h
/usr/include/mirplatform/mir/graphics/egl_extensions.h
/usr/include/mirplatform/mir/graphics/egl_resources.h
/usr/include/mirplatform/mir/graphics/event_handler_register.h
/usr/include/mirplatform/mir/graphics/frame.h
/usr/include/mirplatform/mir/graphics/gamma_curves.h
/usr/include/mirplatform/mir/graphics/gl_config.h
/usr/include/mirplatform/mir/graphics/gl_format.h
/usr/include/mirplatform/mir/graphics/graphic_buffer_allocator.h
/usr/include/mirplatform/mir/graphics/platform.h
/usr/include/mirplatform/mir/graphics/platform_authentication.h
/usr/include/mirplatform/mir/graphics/platform_ipc_operations.h
/usr/include/mirplatform/mir/graphics/platform_ipc_package.h
/usr/include/mirplatform/mir/graphics/platform_operation_message.h
/usr/include/mirplatform/mir/graphics/renderable.h
/usr/include/mirplatform/mir/graphics/transformation.h
/usr/include/mirplatform/mir/graphics/virtual_output.h
/usr/include/mirplatform/mir/graphics/wayland_allocator.h
/usr/include/mirplatform/mir/input/
/usr/include/mirplatform/mir/input/event_builder.h
/usr/include/mirplatform/mir/input/input_device.h
/usr/include/mirplatform/mir/input/input_device_info.h
/usr/include/mirplatform/mir/input/input_device_registry.h
/usr/include/mirplatform/mir/input/input_report.h
/usr/include/mirplatform/mir/input/input_sink.h
/usr/include/mirplatform/mir/input/platform.h
/usr/include/mirplatform/mir/input/pointer_settings.h
/usr/include/mirplatform/mir/input/touchpad_settings.h
/usr/include/mirplatform/mir/input/touchscreen_settings.h
/usr/include/mirplatform/mir/mir_buffer.h
/usr/include/mirplatform/mir/mir_buffer_stream.h
/usr/include/mirplatform/mir/mir_render_surface.h
/usr/include/mirplatform/mir/module_properties.h
/usr/include/mirplatform/mir/options/
/usr/include/mirplatform/mir/options/option.h
/usr/include/mirplatform/mir/options/program_option.h
/usr/include/mirplatform/mir/renderer/
/usr/include/mirplatform/mir/renderer/sw/
/usr/include/mirplatform/mir/renderer/sw/pixel_source.h