fxg to svg conversion is often searched by users that want to convert old Adobe Flash XML graphics files that were originally made using Adobe Flex.
As far as we know, Illustrator is popular choice for such export, simply because it still supports FXG format. But you might as well find dedicated conversion utilities that should be up for this task as well.
Perhaps the successor to the long discontinued Adobe Flex, the Apache Flex might be of help as well.
Updated: November 1, 2023