For GOS 6.0, GOS 5.0 and GOS 4.3 new patch levels are available:
https://www.greenbone.net/en/roadmap-lifecycle/
These maintenance releases fix various open issues for each GOS version.
In total GOS 6.0.8 covers 29 improvements, GOS 5.0.18 covers 27 improvements and GOS 4.3.20 covers 10 improvements.