basic adding of a user in linux and then adding the user to the sudo group to allow it to run super user commands like apt update or other potentially system breaking commands.

Note: replace "username" with your new user account name

with your main root account you can run

adduser username

or if you already have a su added user you can run

sudo adduser username

then to add the user to the sudo group run

usermod -aG sudo username

if this does not work you can try the same command but with sudo, if you are already logged in as root then you should not need to run sudo.

sudo usermod -aG sudo username

then to login to the new account type

su username

or you can logout and then log back into the server