With a Graph window active, press Ctrl+Alt+G to export graph with last used theme without opening the dialog.
After exporting a graph, the file path is dumped to the Messages Log and is clickable to view the exported graph
System Variable to control output to message log.
0 = message with file path
1 = Only dump file path
-1 = no output on messages log
Use the Context menu or Ctrl+Click to open File location in Windows Explorer.
If set @VID=1, click the link in Message Log, it will open with build-in viewer. @VID=1 is by default. It will check file for png, bmp, jpg, emf, then use internal viewer, otherwise still use system