Proxmox on Mac Pro 6,1 (2013) : auto power-on after AC loss not working or how to make it work?

[viraj]

Setup: Apple Mac Pro 6,1 (late 2013 "trash can"), Proxmox VE 9.x installed directly on the internal SSD (no macOS), no UPS.

Goal: Power on automatically when AC returns, including after a manual shutdown.

Tried:

• Booted a separate macOS SSD, ran sudo pmset -a autorestart 1 (pmset -g confirms), then swapped back to the Proxmox SSD.
• Cut wall power while running, then restored it: no fans, no LEDs, nothing.
• SMC reset, then repeated the test: same result.
• Hardware is fine; it boots normally from the front power button.
• WoL doesn't apply as far as I know (Macs only support it from sleep, not full power-off).

Questions:

1. Can "power on after AC restore" be set from Linux on this hardware (e.g. an Intel PCH register via setpci)?
2. Is autorestart known to be unreliable on the 6,1?
3. Any EFI/NVRAM/SMC approach that works without macOS?