OK, what was missing here was:
All good now until the DHCP message in UI again.
Create DHCP Settings for macac1f6b70fb6d.dev-farm.TLD.net task failed with the following error: ERF12-6899 [ProxyAPI::ProxyException]: Unable to set DHCP entry ([RestClient::NotFound]: 404 Not Found) for proxy https://vmforeman-dev.dev-farm.TLD.net:8443/dhcp
This makes me think it’s “just” something with internal SSL communication?