Welcome to the forum @pmi
Is the “same network” trusted enough to just point web browser to headless server Duplicati install?
If not, ssh can tunnel from the system with monitor to the system without, and come in on localhost.
Coming in directly might need some firewall change, and you might need webservice-interface=any.
Remote access to headless ubuntu install was a recent example that needed some firewall tweaks.
Topic was located using the search box at the top of the forum screen, and there were some others.