Proxmox OS (Linux based)
BIOS version FNCML357.0055.2021.1202.1748
UPS through USB cable (data connection)
Description
When launching the shutdown command (shutdown and halt) from within Proxmox (Linux based), the system automatically restarts after a few seconds when connected to UPS (through USB port)
The NUC shuts down normally when not connected to UPS
Resolution
Press F9 to Load Optimal Defaults.
Press F10 to Save and Exit.
Boot into your Operating System.
Press the power button, which triggers proper OS shutdown.