for some reason (e.g. security) I use static IP addresses for most of my equipment.
Here in the community I found this about 2.5 years old question that was never answered: https://support.hifiberry.com/hc/en-us/community/posts/360001477545-Static-IP-Configuration-?input_string=Static%20IP
The there mentioned configuration file /etc/dhcpcd.conf is not available under the most recent Hifiberry OS. There is /etc/network. But within there is only one file 'interfaces.bak'.
So the question remains: is it possible to use a static IP address for the wired connection (ethernet) and how can this be configured?