To give you an idea what is there for cheap arm devices, i looked into that recently and now use a NanoPi R1 -1gb. It works surprisingly well for simple blocking in my tiny amateur home network. Doesnt have 2 GB ports, but one gbps and one USB2Ethernet adapter (~300mbps). There is also another 100mbps port. Should you be tempted read the installation guide first and think about how you deal with the RNG.
In theory the NanoPi R2S sounds better with its dual gpbs, but its not supported, likely due to ARM being a massive pain. If you are however bored and like to tinker you could try porting it yourself. Last i checked there was a working version for OpenWRT, so that might be a starting point https://github.com/jayanta525/openwrt-nanopi-r2s
https://forum.openwrt.org/t/nanopi-r2s-is-a-great-openwrt-device/65374
If you go for it, check if there is any progress already ARM SBC Support Discussion
Also:
Openbsd : https://www.mail-archive.com/arm@openbsd.org/msg01940.html
U-Boot http://u-boot.10912.n7.nabble.com/PATCH-rockchip-rk3328-Add-support-for-FriendlyARM-NanoPi-R2S-td421007.html
Tests with Armbian https://www.cnx-software.com/2020/10/18/nanopi-r2s-nanopi-neo3-tested-with-armbian-thermal-test-ethernet-and-usb-performance/