https://datasheets.raspberrypi.com/rpi4/raspberry-pi-4-reduced-schematics.pdf
: True Gigabit Ethernet is implemented via the Broadcom BCM54213PE PHY, which connects directly to the SoC’s RGMII interface. The 40-Pin GPIO Header Raspberry Pi 4 Model B Full Schematic
Understanding these schematics empowers developers to confidently diagnose board failures, optimize thermal and power performance, and design custom expansion HATs that maximize the potential of the Raspberry Pi 4 ecosystem. https://datasheets