Tried that path and that seems to have fixed it.
● mailmanweb.service - GNU Mailman Web UI Loaded: loaded (/etc/systemd/system/mailmanweb.service; disabled; preset: enabled) Active: active (running) since Mon 2025-10-27 14:18:42 EDT; 25min ago Main PID: 107897 (gunicorn) Tasks: 4 (limit: 8814) Memory: 163.4M (peak: 163.9M) CPU: 4.060s CGroup: /system.slice/mailmanweb.service ├─107897 /opt/mailman/venv/bin/python3 /opt/mailman/venv/bin/gunicorn -c /etc/mailman3> ├─107898 /opt/mailman/venv/bin/python3 /opt/mailman/venv/bin/gunicorn -c /etc/mailman3> ├─107899 /opt/mailman/venv/bin/python3 /opt/mailman/venv/bin/gunicorn -c /etc/mailman3> └─107900 /opt/mailman/venv/bin/python3 /opt/mailman/venv/bin/gunicorn -c /etc/mailman3>
Oct 27 14:18:42 dap002 systemd[1]: Started mailmanweb.service - GNU Mailman Web UI. Oct 27 14:18:43 dap002 gunicorn[107900]: Updated PYTHONPATH to : /opt/mailman3/venv:/etc/mailman3 Oct 27 14:18:43 dap002 gunicorn[107899]: Updated PYTHONPATH to : /opt/mailman3/venv:/etc/mailman3 Oct 27 14:18:43 dap002 gunicorn[107898]: Updated PYTHONPATH to : /opt/mailman3/venv:/etc/mailman3
Now when I try to access it (http://localhost/mailman) I get a 404 error.