We're sorry about the trouble with Lightroom. Would you mind sharing the exact version of Lightroom you're using along with your computers operating system? What export settings are you using to save the files? Are you getting an error?
You can try re-installing the app using the Creative Cloud desktop app to check if that helps. If the issue persists, try resetting the Preferences of Lightroom by launching the app while pressing & holding the Shift + Option keys (on Mac) or the Shift + Alt keys (on Windows).
Are you using MacOS Catalina or Big Sur, perhaps? If so, you must give Lightroom permission to access the desktop in the System Settings. The screenshot shows Lightroom Classic, but the same applies to Lightroom (cloud).