TA-DA! The Belkin USB adapter works with QEMU via USB passthrough
The Belkin is connected via Ethernet to a Linux computer.
The Belkin is connected via USB to a Linux computer.
USB is passed directly to QEMU/AmigaOS4
The Linux computer has internet access via Wi-Fi
AmigaOS4 uses the Belkin USB adapter as its default network card.
Command line for connecting the device to QEMU
-device usb-host,hostbus=0x003,hostaddr=0x005
Here is the data for the Linux side
Bus 003 Device 005: ID 050d:0121 Belkin Components F5D5050 100Mbps Ethernet
Here on the AOS4 side
[USB] INFO | "hub.usbfd" | "HUB" | Device on hub port 1 attached as fkt 0x6FF8FF00 (ifc 0x6FF43CC0)
[USB] INFO | "USB Fkt Init" | "Init Fkt" | [fkt 0x6FF8FF00] Fkt is {Vendor: 0x050D, Product: 0x0121, Class: 00.00}
[USB] INFO | "USB Fkt Init" | "Init Fkt" | [fkt 0x6FF8FF00] Fkt ("ADMtek","USB To LAN Converter","0001") initialized
[USB] INFO | "USB FD Starter" | "Sys_EndInitialAttachmentPhase" | Initial USB Attachment Phase terminated
[USB] INFO | "USB FD Starter" | "Bind FD" | No driver found for fkt 0x6FF8FF00/ifc 0x6FF43E40 {Class 00.00}
Test carried out on QEMU9 PEG2 – I’ve been testing it locally since yesterday and it’s working. It’s not exactly lightning fast, but it works ;-D

Screenshot description:
On the right, in the background, tcpdump running on Linux ETTH
On the left, Linux debug windows and the ‘serial_client.py’ window from the qemu-runner package