Generally a prefab workflow is not supported for a couple of different reasons.
Firstly there is only supposed to be a single AstarPath component in the scene at any time. Typically what you would do with prefabs is to create them and then have multiple in the scene.
Secondly things like storing graphs in prefabs is not supported due to limitations of the Unity serialization system. It is technically possible, but the large amounts of data makes the Unity editor slow down to a crawl. It was possible a long time ago, but when Unity rewrote their Undo system it got a lot slower when you had to serialize a large amount of data. You can save/load graphs from files however, see: https://www.arongranberg.com/astar/docs/save-load-graphs.php
If there’s some useful workflow that you think should be implemented I’m open to suggestions though