How to download Backup files to local machine

What exactly do you mean with "local storage system"?

You can generally download files from the PBS Webinterface via the file explorer (under your datastore > Content) by clicking the small folder icon when you expand the backup group. This only works for file-based backups done with the proxmox-backup-client or container backups.

If you want to restore the files from a VM you can do so through the Proxmox VE WebUI by selecting your pbs-storage > VM-backups and then File Restore.