I do not use archive or backup features in SP, had mixed results may years ago with doing this...ended up missing a bunch of either custom symbols or textures or something.
I'd use File Explorer and just backup the whole SoftPlan 2018 directory. I have a remote office twice/week so I sync over 2 PC's and 1 laptop for SoftPlan 2018 directory and my projects directory and it works great. With the speed of copying files and the size of storage drives its easy and fast. In the event of a corrupt anything in the Softplan 2018 just delete the whole directory and copy the new one from the storage location....NOTE:just keep your storage copy fairly current to prevent loss of custom symbols, notes or anything else you may add.
not a plug for GoodSync, however its what i use. whenever i connect back into the home network it begins to sync my 3 computers and in a matter of a few minutes the SP root folder and my job folder are equal on all pcs.