Find out why your project is not exporting.
Likely you’ll have an error message or Final Cut Pro will crash - “Final Cut Pro quit unexpectedly”
If you have a warning containing a “frame error” message or a “rendering error” message. View this video: How to fix & clear export error messages; https://youtu.be/r6JmPGyno0A
Otherwise there could be a number of issues that are causing the export to fail or Final Cut Pro to crash on Export.