Support was added with IPFire 2.27 - Core Update 164
The NanoPi R4S (as "R4S") is a FriendlyElec mini-router with edge-computing and dual Gbps Ethernet ports. Its dimension is 66 mm x 66 mm. The NanoPi R4S uses Rockchip's RK3399.
IPFire using the Serial Port at baud rate of 115200 n8. The R4S connects via a 3.3V TTL, 3-pin 2.54mm pitch connector.
Note: If you have problems booting without the serial interface connected, add a 10k ohm resistor between GND and RX.