1 You can’t install macOS
If the App Store installer won’t work properly, make an external bootable installer from it on a USB flash drive or SSD using instructions at . To start a T2 Mac up from that, first start up in Recovery and enable it in Startup Security Utility. On an M1 Mac, start up in Recovery, select the USB drive there and start up from it. If that fails, use the Install macOS feature in Recovery instead, although that only installs the latest version of macOS.
