The graph file extension is related to the GraphSLAM and used for its data files.
GRAPH file extension - GraphSLAM data
What is graph file? How to open graph files?
File type specification:
The graph file extension is associated with the GraphSLAM, a simultaneous localization and mapping algorithm used in the robotics.
The graph file stores various data used for internal purposes of the GraphSLAM.
This graph file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.