I would like to login as root, but I cannot find a way to enable manual login on Elementary OS.
First read this article just to learn the basis. https://www.redhat.com/sysadmin/sysadmins-dont-sudo
Then the best idea is to type sudo visudo and add yourself to the root group or wheel (Red Hat, CentOS, Fedora).
You must read about the visudo command and how to make a user as an additional root admin in the system.
I do not want to write an elaborate.
Just for your information that it is not secure. Probably, I did not check it, there is a need to edit a .profile file or .bashrc file to make it work. But I need to check it.
Anyway it this is really bad idea, because you may just screw your system. Root is God and God can create and destroy.
There is no need to run as root every day with elevated permissions. This way you will run every app as root and simple java script during browsing the Internet with any browser will be able to harm your system because of elevated level.
We use su or sudo. I usually use:
sudo su -
To work as root in terminal.
But this is for experienced users. I do not recommended to work as root for inexperienced user.