Problems with faulty update installer boot I'm having a problem with a macOS update. In short, I downloaded the update that requires a system reboot. But this happens: at boot time the machine starts the update installation disk, the installation starts but a moment later a warning appears telling me that there are problems and the installation of the update then fails. Restarting the machine I find the machine re-doing the same update again (which will fail).

So the only way I can start the machine and use it is to hold down the ALT button at boot time and then select the usual boot disk.

I had a similar problem a few years ago, but I can not remember the procedure that allows me to remove the faulty installer from the list of boot devices.

Can anyone suggest something useful? I also remember that by removing the faulty installer and re-downloading the update then I was able to correctly update the operating system.
From AppleToolBox.com:


  Fixing macOS Install Problems in Recovery Mode
  
  To get to recovery mode on your Mac or MacBook, you will need to press and hold Command+R keys together when booting up your computer.
  
  Once you are in the Recovery mode, click on the Apple logo on the top left corner of the screen and make sure that your startup disk is pointing to the Mac Boot disk.
  
  Now find the macOS update program and run the update. Sometimes, when you are facing install/upgrade issues, a workaround that works for many users is to create an external bootable installer and try to run the install program using it. Apple provides a detailed white paper on this process. You can create the bootable installer on a USB and then try it to update the macOS.