[Solved] just had to log out and back in Original post: I'm running Debian 12 and I set a separate root password from my username password.

When trying to install a .deb file I noticed that it said I was not in sudoers file so I looked it up and tried the command SU and successfully entered my root password.

The I tried doing

sudo usermod -aG sudo [username]

And then I verify the addition of the user to the sudo group with

groups [username]

And this does indeed show that I am in the sudo group however when I try to install a .deb file after that or even sudo apt update its still telling me I am not in sudoers list.

Any ideas what I'm doing wrong here?