Changed root pw with root account disabled and now my password isn't recognized

[ilikelinux]

Here I explained what exactly went wrong:

My user is suddenly "not in the sudoers file"!?

I got cached with the same issues, when I tried a long while ago the same. Useradd -G has missing logic, to tell you when you try to add an existing user, alias you would have to list the existing groups you already have been member of. man useradd: -G, --groups GROUP1[,GROUP2,...[,GROUPN]]] A list of supplementary groups which the user is also a member of. Each group is separated from the next by a comma, with no intervening whitespace. The groups are subject to the same …

In your case, if your user is moved just in one group, the solution from @ersen is not helping you. Because you are moving yourselves just to one group again.

Unfortunately “sudo usermod -G input myusername” is not preserving your existing elevated groups (like wheel) … just puts you in the group you ask for additionaly.