Please see message below originally posted by @mitsudome-r on Autoware Discord:
As announced in the Autoware GitHub discussions, we have upgraded the main branch of Autoware to ROS 2 Humble, and we no longer support Galactic in the main branch. Please follow the latest Documentation to install the newest version of Autoware.
GitHub Discussions: Timeline for ROS Humble Transition · Discussion #2622 · autowarefoundation/autoware · GitHub
Autoware Latest Documentation: Source installation - Autoware Documentation
We also created the galactic branch for people who still need to transition to Humble. However, we will not merge the latest features into the galactic branch, so we strongly recommend that you transition to Humble as soon as possible. Galactic branch: GitHub - autowarefoundation/autoware at galactic Autoware Documentation for Galactic: Source installation - Autoware Documentation