A Google search seems to indicate that this mini PC uses a NIC that is not yet supported in Linux (the Motorcomm YT6801 Gigabit Ethernet Controller). I could not confirm that from the manufacturer's web site, but saw that in a forum. If that's the case (and maybe you can firm?) then I would go with a USB to ethernet adapter for the initial install. After installation, you can try to enable the built-in YT6801 NIC by:
1. Checking if your kernel (in Proxmox 9.0.1) already has support or you need to build the module (you can try modprobe yt6801 or checking for lsmod | grep yt6801).
2. If not present, fetch the driver source (for example from GitHub or Motorcomm) and compile it as a kernel module (DKMS style) for your current kernel.
3. Load the module, configure the interface, test connectivity, then swap over from USB-NIC → built-in NIC (if successful).
4. Evaluate if the built-in NIC is stable enough for your use case