Need help to backup in external HDD

Hello everyone, i need your help. I have an external hdd, Toshiba Canvio Advanced, and i need it to backup my Nextcloud folder.

The problem is that when i need to find the Nextcloud folder, in Toshiba Backup Software, it isn’t there, i can’t find it.

I’ll appreciate any help. I need to backup in my external hdd so i can have the information in a place without internet conection.