I could solve it myself:
I could publish topics from SImulink and subscribe in ROS/Unreal by:
1) Check the IP address of the Windows seen from Ubuntu by "ip route show | grep -i default | awk '{ print $3}'"
2) Set the IP address as the Node Host IP address of the ROS network setting in SImulink.
However, it turned to be impossible to subscribe topics from ROS after i did solve the problem above. The topics are published to ROS and i can echo them in Ubuntu terminal, but the ROS Subscribe block in Simulink receives nothing.
I have no idea what causes this issue. The only change from the case i could subscribe topics in Simulink is the Node Hos IP Address, and it did not work even when i return it to be "localhost".