TL;DR

• EDK2 boots a real UEFI environment on the RK3576 — swapping out U-Boot proper for EDK2 after BL31, verified on two boards (Radxa ROCK 4D over SPI, ArmSoM CM5-IO over SD).
• HDMI’s worst bug was the debugging itself: reading overlay registers back after enable — read-only, no writes — silently perturbed VOP2 and killed the picture; the one real fix underneath all the phantom bugs was a register-write-ordering issue.
• USB needed two DWC3 xHCI workarounds: skip a structurally-redundant EvaluateContext on SuperSpeed, and mark the hub slot-context flag before the interrupt endpoint arms, or the onboard hub never enumerates.
• eMMC was simply held in hardware reset — EMMC_RST_N defaults to 0, and RK3588 boards never notice because SPL boots from eMMC and clears it in passing; RK3576 booting SD/SPI never touches that bit at all.
• Ethernet’s PHY part number was copy-pasted wrong everywhere — four independent sources call it an RTL8211F; the schematic says MotorComm YT8531C. It works either way (both are generic Clause-22 PHYs), until you need PHY-specific tuning.
• Two firmware/OS handoff bugs lived below any single peripheral: a coincidental MZ byte pair in unrelated memory crashed the OS-loader scan, and an unpopulated RAM bank register read as all-zero decoded into a phantom 256 MB.