Due to this manual, if you run sitl in standalone mode, it will work with the gazebo server in the same network, however, it just constantly spawns [gz_bridge] Service call timed out as Gazebo has not been detected.
I ran a PX4 instance with PX4_GZ_STANDALONE=1 make px4_sitl gz_x500 on 192.168.1.1 and the Gazebo server with gz sim -r on 192.168.1.2.
When i run gz server on the same host, everything works perfectly. Also on 192.168.1.2 i have a ROS agent that connects with PX4 instance, so its not a networking issue.