User reports s/he can't open zip files created from a backup or export with another app.
thanks for reaching out and sorry about the issue. The .zip files you're looking at are actually files in GoodNotes format. They can only be opened by GoodNotes for iOS or GoodNotes for Mac. If you want to open the files with other apps, please back them up or export them as PDF. You can set the file format to PDF in the export options or in the settings of the automatic backup. Setting a different file format when using "Backup All" is not yet supported.