Why is a backup mapped as a network drive a risk?
Because ransomware encrypts every drive it can reach, and a mapped drive looks to it like any other folder. If a backup target is permanently mapped on a server or workstation, or reachable over a share with the same credentials, the ransomware on that machine will encrypt the backup files along with everything else, and the backups are gone at the moment you need them. The same applies to an external USB disk that stays plugged in, and to sync tools that mirror every change, including encryption, to the backup location. Better: let the backup software write to its target with its own service account that ordinary users and servers do not have, keep the target off the list of shares people browse, and add an immutable or offline copy. A quick check today: look at which machines have a drive letter or share pointing to the backup storage, and remove the ones that do not need it.