The 'Backup' procedure in v10 that is set to occur when you exit Lr-Classic will save the YourCatalogName.LRCAT file in the Backup ZIP file. In the latest Version-11 of LrC this has changed slightly to also now include a new file - YourCatalogName.LRCAT.LRDATA that holds information about the new Masking edits.
So, now with v11, the Backup ZIP contains two files- ...LRCAT and ...LRCAT.LRDATA
It DOES NOT BACKUP ANY PHOTO FILES (Pictures) ..!! That is your responsibility using methods outside of LrC.