I had a Mac recently that had been wiped via Find My, so it had neither an OS nor the recovery environment on the internal drive. It also had the default firmware settings that didn’t allow booting from external media. Although I have all of the recent macOS installers on a USB SSD, I couldn’t boot into them due to security settings. I couldn’t use the Startup Security Utility from the recovery environment as you need to enter the admin credentials for a local user, and there were no local users.

To further rub salt into the wound, booting into recovery took me to High Sierra, and although I could get into recovery, I was unable to install the OS; It kept coming up with an error message: “The Recovery Server Could Not Be Contacted”

Fortunately Mr Macintosh found a number of solutions, as well as digging in to find the root cause of the issue: