Please make sure that the export path you are writing out to is readable and writable by Topaz Video and that the path exists.
Try adding Video to the list of apps with ‘Full Disk Access’ in the macOS System Settings and restarting the app after.
System settings > Privacy & Security > Full Disk Access
If this does not work, please proceed to a clean install which should reset the app’s permissions.
If you have any custom presets saved, you will want to copy them over to a different folder (e.g. desktop) as they will get deleted when you uninstall.
Applications > Topaz Video AI > right click and Show package contents > Contents > Resources > Presets
Uninstall Topaz Video AI by dragging and dropping the app into the trash bin