Realtek 2.5g RTL8125B Odroid H2+

Has anyone installed OpenWRT on the Odroid H2+?
It uses Realtek 2.5G ethernet NICs and the snapshot from yesterday (2020.07.16) doesn't recognize these NICs.
There seem to be drivers for linux, but I haven't tried them in openWRT (hard to do when ethernet isn't working...)
The Odroid H2+ looks like a really good option for a 2Gbps router.

Try to install kmod-r8169.

I'm trying to install kmod-8169.
No network so I can't use opkg install.
I then try a usb drive, but I can't mount it without mkfs, which needs to be installed.
I also try to use various usb network adapters, but I can't get a network connection.
Any thoughts as to how to do this?

Ubuntu with OpenWrt in a VM of some kind to find the right bits?

Not sure what you mean, but I've got the "bits" - I downloaded kmod-8169 elsewhere.
I can't get it to the Odroid-H2+ to install it.

Then is a complete image via Image Builder an option, at any rate that is really not the driver you want is it, although it may work to get things going.

That looks like it might work.

What is the right driver?

This, but I assume it is not in OpenWrt as of yet, so there will be some work to get that into the tree. Which is the reason I suggested you may want to start with some flavour of debian to get things working.

Thanks for the info.
Since I want to do performance testing and I assume that the older driver won't work very well, I'm going to try the Ubuntu approach in the hopes that it approximates the routing performance of the eventual bare-metal OpenWRT with updated 2.5G drivers.
Our ISP is going to offer a 2Gbps option, and we're looking for reasonably inexpensive router/firewall that can support this. pfSense and opnSense seem unlikely to get updated drivers for the 2.5G realtek any time in the near future - BSD people seems to really hate Realtek, if one believes the forums.
Are there any other inexpensive routers that support > 2Gbps interfaces and that run OpenWRT?

Well, it's not true that BSD people seems to really hate Realtek. OpenBSD supports RTL8125/RTL8125B: