Reboot directly from MacOS to Startup Manager? (Init command) I have a strange setup (briefly, I have Windows 10 on an external SSD and I use a MacBook Pro as my main Mac these days in a dock that connects to an external monitor which has a hub - Samsung CJ79 34" - everything, including the SSD, is plugged into the monitor).

Because of this strange setup I can only change startup disks via the Startup Manager - I can't boot directly from the Startup Disk control panel.  However, my Windows keyboard doesn't work to change desktops I need to plug in my original Apple keyboard.

Knowing that MacOS is basically a heavily modified UNIX setup I hazard to guess there is a command somewhere in the OS (like the init command) that will let me boot directly from MacOS to the Startup Manager screen.

Does anyone know what this is and if it is possible?  Thanks.
A few days ago, I had a problem to reboot on the recovery-mode (CMD+R) and to also to have access to the startup manager (Option/Alt). None of those key combinaisons would work for me. So after some research, I found out how to boot in any drive without the startup manager.  



(Solution 1) Reboot directly onto a USB drive or another partition without the startup manager:
You just need the macOS application Boot Manager. Once installed, it appears in the menu bar, just like the image below. You can  then select the drive that you want to reboot onto.


Here is a tutorial on how to install it: Boot Manager installation tutorial

Note: At some point, you will need to reboot into the recovery-mode. So you can use the following trick 


Open a terminal
Type in: 


  sudo nvram recovery-boot-mode=unused

Enter the admin password
Restart the computer. It will automatically reboot into the recovery-mode




(Solution 2) Replace the startup manager: You can replace the startup manager with an application (just like rEFIND) that will ask you to select the drive to boot onto without having to press the "Option/Alt" key when booting up your computer. The app is Next Loader and is from the same dev. The installation tutorial is here.