The dreaded old “Export Result: An unknown error has occurred” problem has reared it’s ugly head in my workflow. It isn’t related to the particular file I’m working on. I thought I had fixed the problem by uninstalling Glyphs, emptying the trash, and reinstalling glyphs, but the problem comes back after I’ve exported a few times. I can always fix the problem (temporarily) with the delete/empty/reinstall process. The last version of Glyphs that worked properly was 3316. I am currently using 3260 with Sonoma 14.5.
Can you try the latest cutting-edge version? You can install multiple versions of Glyphs side by side by downloading other versions from Glyphs Versions.