How to make a user sudo in ubuntu 20.04

With a root user or with sudo privileges execute the following:

sudo adduser username sudo

Example:

ubuntu@vmrp01ubuntu2004web:~$ sudo adduser operatorvm sudo
Adding user `operatorvm' to group `sudo' ...
Adding user operatorvm to group sudo
Done.
ubuntu@vmrp01ubuntu2004web:~$

In this case, the 'operatorvm' user is required to log in to take advantage of this privilege.