Update to the former post: Tons of new features have been added to mola + mola_lidar_odometry in the latest releases:
- Correct handling of ROS 2 namespaces.
- Support for NDT-3D maps
- ROS 2 services to start/stop mapping, load/save maps, etc.
Resources:
- Step-by-step tutorial: MOLA-LO: Build a map and then localize — MOLA v1.9.1 documentation
- ROS 2 API docs page with available services, /tf frames, topics, etc.: ROS 2 API — MOLA v1.9.1 documentation
- LinkedIn post: ✨ MOLA-LiDAR Odometry 0.4.1 & ✨ MOLA 1.4.0 have been released to #ROS2 with tons of news! | Jose Luis Blanco Claraco
- YT video following the tutorial:
Feedback, issues, or PRs are all greatly appreciated! 
PS: Not all these features are available in the current binaries from apt… you might need to build from sources or wait for the next release cycle.