Why would you expect USB3 and Ethernet, fast and relatively expensive interfaces, to be attached to a cheap low-spec MCU?

Did you consider a ready-made USB3 extender over Ethernet? There is a reason they cost so much ;-/

Rockchip SoCs starting with the RK3399 can do both USB3 and Ethernet.

The only board that I own that does both at the same time is the Pine64 Quartz64 that uses the RK3566. My Pinebook Pro doesn't have an ethernet port, Orange Pi 5 Max has ethernet but doesn't use the builtin controller to provide it.

I use NetBSD on a Pine64 RockPro64 and use USB3. It has been stable:

    awge0: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
            ec_capabilities=0x1<VLAN_MTU>
            ec_enabled=0x1<VLAN_MTU>
            address: 26:80:xx:xx:xx:xx
            media: Ethernet autoselect (1000baseT full-duplex)

i see Quartz64 with 4GiB of RAM offered for $60. Sounds pretty reasonable for an SBC of this caliber. I mostly mean that something like the original RPi would be underpowered for USB3.0 and 1GbE, to say nothing of smaller devices like a $15 ESP32.

Pi4 does two USB 3.0 ports, but you are right in that USB 3.1 is a little much for a SoM.

Its a nice little SoM, in some ways it was better than the pi5 for hardware media encoding. =3