Rebooting could be a mini-game where you dodge the user's BIOS keystrokes a few times before they give up
sudo systemctl reboot --firmware
shutdown /r /t 0 /fw
These reboot directly into BIOS.
For Windows CMD+R menu, run it by pressing CTRL+SHIFT+Enter (elevates to admin). You may have to do it twice for some unknown reasons after reinstalling the OS.