Is there The Way to get into Single User Mode w/o rebooting?
Depending on your needs, try changing the log in window to ask for a user name and then enter >console as the user.

This likely was removed at 10.10 so you’d need to boot to recovery or ssh in or use a terminal app if this legacy init type bypass isn’t what you seek.


http://osxdaily.com/2018/09/02/access-login-console-terminal-mac/


Also, this isn’t true root single user mode, that needs to happen early in the boot process on modern macOS.