In addition, for your reference, when you start the computer, you can select the startup item by holding down the option key until you see the selection screen.

Also, I advise you not to use a USB flash drive, because the USB flash drive that Apple needs to start is not a USB flash drive system disk under general windows. The USB flash drive that Apple can start must be a mass-produced USB flash drive.

In other words, it is not enough to make a USB flash drive, but also to rewrite the chip of the USB flash drive. The computer is initially identified as a USB flash drive, which needs to be identified as a usbcdrom, and then the system image file is added. And not all brands of USB flash drives can be mass-produced. As far as I know, Lenovo's USB flash drive can basically be mass-produced.

Mass production is a long story, please search.

Why don't you do it? It is because Apple computers using I-series cpu, whether all-in-one or notebook, can't install the system even if you are a mass-produced USB flash drive after I-series abandoned the South Bridge chip. Although you can see it at the beginning, you can't start it after you choose it. I don't know this question yet. Anyway, my own mass production is already like this.

At present, Apple's notebooks and old models that can start USB flash drives are only 13.3 inches.