Cannot create new users in Mojave (10.14.6)

I have found a few more topics like this but could not find a conclusive answer. If there is a one, please do let me know.

This is what I have configured:

• 1 normal user
• 1 admin user
• Both exists already from the time I was using Snow Lepoard

When I want to install a program with the normal user I usuallay have the chance to identify as the admin user, this works perfect.

For a stupid program not allowing me to identify as admin I need to login with the admin account: I cannot. The system won't accept my password.

I changed the normal user to admin, that worked using the password that failed to log in. So the password is correct for the admin user, how come I cannot log in?

The idea I had was to create a new admin user and delete the old one but when I create a new user, normal or admin, the home directory is created but the new user doesn't appear in the account list, not even after a restart.

Does this sound familiar to anyone?

Any idea how to resolve or troubleshoot?