In case someone else needs this information
As I understand, DHCP is not available on netcup, and you need to manually specify the IP address, subnet, and gateway for the internet connection.
I managed to set up the internet manually by changing the adapter settings in Windows 2025.
You’ll need the server information from SCP, under the Network tab.
In Windows go to network adapter settings:
Settings -> Network & internet -> Advanced network settings -> Ethernet -> More adapter options -> Edit
For IPv4 I specified the IP and gateway from the SCP settings, and I also set the subnet mask to 255.255.252.0 (since my IP had postfix /22).
I also specified DNS 1.1.1.1 and 8.8.8.8 – you may prefer different ones in your case.
If needed, you can enter IPv6 data based on the SCP information, but this is probably optional (I just unchecked it).
After all this i just rebooted the server.