I'm new to all of this and I had trouble with getting my Raspberry Pi 5 to work with a Ugreen gigabit Ethernet adapter.
In case anyone else has issues getting that adapter to work with the RPI 5 snapshot (only currently supported method at time of writing), make sure to include the following custom packages in the OpenWRT firmware selector build tool:
kmod-usb-net-asix-ax88179
kmod-usb-net-cdc-mbim
I had trouble because I was only using the ax88179 module which wasn't enough.
I've since found out that the TP Link UE300 is a better option apparently and that uses the kmod-usb-net-rtl8152 module .
My AX88179 doesn't seem to need the cdc-mbim...? (Well I included kmod-usb-net-asix-ax88179 which might automatically include the other one), however looking at some older posts, this AX88179 seems to have long term stability issue.
If anyone wants to buy USB one, I recommend to pay a bit more to get 2.5G RTL8125B which is great (because Synology NAS community already has lots of people using this to get 2.5GbE for their NAS so I believe it works great, and in fact many SBC with 2.5GbE also using this), and if one day you decided to move on to other platform the 2.5GbE USB can be used to upgrade your PC or something else.
cdc-mbim is definitely not necessary for any ethernet dongle. But cdc-ncm might be in some cases, and cdc-mbim will drag in that module as a dependency.
I've seen the Club 3D CAC-1420 mentioned. About $40+ so definitely need to have a good use case in mind. There is a lot of advise against USB ethernet adapters out there but the two I mentioned seem to work for me. My ISP's upload speed is 40Mbps so probably not enough to stress these adapters enough.
I'm surprised that a Realtek chipset is recommended as the general advise is to avoid them (maybe that's more relevant in the PCIe NIC space though).