Dear Lingd,
that's interesting to hear as the code of the Simple Backup Plugin was merged with the main app some time ago. If there's no "Backup" entry under "Plugins" in the menu "Tools/Options", fresh installations of Joplin Portable (mine was done some time ago) probably come without the backup plugin. If there's no backup folder somewhere else in the same directory where "JoplinProfile" is located, then there's probably no plugin in place.
I'd still recommend installing the Simple Backup Plugin though: It allows for automated backups, and you can specify the storage location of the "JoplinBackup" folder.
All the best again
former_evernotist