How can I check what middleware I am using in ros2?

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There is info you can use:

https://docs.ros.org/en/galactic/Conc...

The ROS 2 binary releases for currently active distros have built-in support for several RMW implementations out of the box (Fast DDS, RTI Connext Pro, Eclipse Cyclone DDS, GurumNetworks GurumDDS). Since Galactic, the default is Cyclone DDS, which works without any additional installation steps, because we distribute it with our binary packages. Prior to Galactic, the default was Fast DDS, which works without any additional installation steps.

If you didn't change anything there, you should have default RMW.

For practical information on working with multiple RMW implementations, see the Working with multiple RMW implementations” tutorial.