Hello @Kreace ,
Facing the same need as yours, we also wrote our own ROS 2 launchfile to launch a Gazebo simulation with an Iris running PX4, communicating over ROS 2 and controlled over QGroundControl.
We would love to contribute it to the PX4 codebase or share it with you if you still need a launchfile.
The only issue that keeps us from doing so is that since, as @TSC21 said, PX4 does not at the moment build as an Ament package, it does not install its executables and resources to a ROS 2 workspace so we had to hard-code the location of the PX4 codebase to find the executable.
We would be happy to share this launchfile with you, and if you hopefully had some time on your hands to help make PX4 build as an Ament package, it would become possible to use get_pkg_share_directory to retrieve the stuff instead of a hard-coded path and thus make this launchfile available to the larger PX4 community by contributing it.
As I already said, we would love to contribute this launchfile, the only thing is that since we got it working for ourselves we do not have enough time on our hands to modify the PX4 build system to be able to contribute it. We are a very small team.
Please let me know if you are interested.