External_url not possible to set from UI (solved)

I have a super fresh 2021-12 installation from scratch.
The configuration.yaml is pretty empty:

# Configure a default setup of Home Assistant (frontend, api, etc)

group: !include groups.yaml
automation: !include automations.yaml
script: !include scripts.yaml
scene: !include scenes.yaml


Setup basic information - Home Assistant states, this is the way, if you want to edit stuff in UI. Which is what I want.

However my UI looks like this:

In the UI I can not set up the base_url, external_url or whateever.
duckdns and letsencrypt up and running with no issues.

Some ideas what might be wrong?

Got it: In user config “advanced mode” needs to be enabled.