CWWK Intel-N100 MiniPC (Intel i226-v): wrong speed on ETH1-Port

[XXXBold]

Hi

I have e issues with the network config on the ETH1-Port (The Device has 4 ports, 0..3). This is my device: https://cwwk.net/products/12th-gen-...-4800mhz-4xi226-v-2-5g?variant=44614005555432

I haven't setup anything unusual afaik, here's my proxmox network config:


I've tried different cables (the same that work on 2.5G on other ports), so that's not an issue.

Here's the output of ethtool:

ethtool enp2s0 (ETH0 port, This is a LAN port (management of proxmox), which is configured to fullspeed (connected to 2.5G USB-Adapter))
Settings for enp2s0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
                                2500baseT/Full
        Supported pause frame use: Symmetric
        Supports auto-negotiation: Yes
        Supported FEC modes: Not reported
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
                                2500baseT/Full
        Advertised pause frame use: Symmetric
        Advertised auto-negotiation: Yes
        Advertised FEC modes: Not reported
        Speed: 2500Mb/s
        Duplex: Full
        Auto-negotiation: on
        Port: Twisted Pair
        PHYAD: 0
        Transceiver: internal
        MDI-X: off (auto)
        Supports Wake-on: pumbg
        Wake-on: g
        Current message level: 0x00000007 (7)
                               drv probe link
        Link detected: yes
        
ethtool enp3s0 (ETH1 port, This is a LAN port, which is configured to 100M (connected to 2.5G USB-Adapter))
Settings for enp3s0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
                                2500baseT/Full
        Supported pause frame use: Symmetric
        Supports auto-negotiation: Yes
        Supported FEC modes: Not reported
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
                                2500baseT/Full
        Advertised pause frame use: Symmetric
        Advertised auto-negotiation: Yes
        Advertised FEC modes: Not reported
        Speed: 100Mb/s
        Duplex: Full
        Auto-negotiation: on
        Port: Twisted Pair
        PHYAD: 0
        Transceiver: internal
        MDI-X: off (auto)
        Supports Wake-on: pumbg
        Wake-on: g
        Current message level: 0x00000007 (7)
                               drv probe link
        Link detected: yes
        
ethtool enp4s0 (ETH2 port, This is a LAN port, which is configured to fullspeed (connected to 2.5G USB-Adapter))
Settings for enp4s0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
                                2500baseT/Full
        Supported pause frame use: Symmetric
        Supports auto-negotiation: Yes
        Supported FEC modes: Not reported
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
                                2500baseT/Full
        Advertised pause frame use: Symmetric
        Advertised auto-negotiation: Yes
        Advertised FEC modes: Not reported
        Speed: 2500Mb/s
        Duplex: Full
        Auto-negotiation: on
        Port: Twisted Pair
        PHYAD: 0
        Transceiver: internal
        MDI-X: off (auto)
        Supports Wake-on: pumbg
        Wake-on: g
        Current message level: 0x00000007 (7)
                               drv probe link
        Link detected: yes
        
ETH3 is passed through to a opnSense VM (WAN-Port) on a 1G connection which seems to work.

How can I get ETH1 to work at fullspeed/1G too? I've tried https://www.shellhacks.com/change-speed-duplex-ethernet-card-linux/ but it doesn't have an effect.

Thanks & Regards,
XXXBold