How to login as "root"?

If you are a developer this article might give help : How to enable the root user on your Mac - Apple Support

But for everyday routine work on Mac computer there is " NO " need to log in in root user account .

I would question why?

The user (admin) account by default is not the super user (root) account. This is a security feature on the mac—by design.

sudo is a tool that is provided to allow regular (non-root) users to perform root tasks on a case by case basis from the terminal.

please note password will not echo.

Using the sudo command in Terminal requires a non-blank administrator password - Apple Support

https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPag es/man8/sudo.8.html

I have not enabled 'root' on any computer in years, rather doing things via 'sudo', and I'm speaking as someone that has been using Unix since the mid-80's when I would always have at least one terminal session logged in as 'root' 24/7.

The sudo command has eliminated that need for 99 44/100% of my needs.

You have been given information on how to enable 'root' if you desire, but if you give us information on what you want to do as 'root' perhaps we can offer some useful alternatives.

NOTE: 'root' is a well known username on all Unix systems. If you have your Mac directly on the internet with ssh enabled (System Preferences -> Sharing -> Remote Login), and look at your console logs, you will see repeated attempts to break into your Mac by guessing the 'root' password. This is one of the reasons 'root' is not enabled by default.

Root is disabled by default.

Read this thoroughly before you decide to enable root.

How to enable the root user on your Mac - Apple Support