No admin account in macOS
When launching single-user mode, you're informed with the following text that you need to mount the disk as writable before you can make changes.


Root device is mounted read only

If you want to make modifications to files:
        /sbin/fsck -fy
        /sbin/mount -uw /



This text is printed when you launch single-user mode. Do as it says to mount with write access.