Access to duplicati backup off-prem files from another computer

how can I access the data (to be able to restore them) on another computer, other than the one on which the backup is done ?

You need Duplicati installed on the alternate computer. If it’s just a one off restore, you would go to Restore and pick “Direct Restore from Backup Files”. You would need to enter all the relevant data: destination, path, authentication credentials, encryption key, etc. At that point Duplicati will download files needed to display a restore directory tree where you can choose what files to recover.