To clarify, 'apt update' updates the repository to see if upgrades are
available. 'apt upgrade' installs any available upgrades.
In the comment you refer to, I suggested running both commands because you
had already installed youtube-viewer and I wasn't sure if it was the latest
version. Here, ran 'apt-update' before installing youtube-viewer, so it was
already the latest version.
Running 'apt upgrade' installs all upgrades for programs you have installed,
not just youtube-viewer, which is why you might get message related to other
upgrades, like the grub config file.
youtube-viewer has some recommended and suggested packages. It's generally
not a good idea to install all of them because you might end with a bunch of
crap you don't need, but it's possible that I have one installed that you
don't and that is why it works for me and not you, so let's install the ones
I have installed and see if that helps.
$ sudo apt install liblwp-useragent-chicaching-perl
liblwp-protocol-https-perl libtext-charwidth-perl libterm-readkey-perl
libencode-perl mpv vlc wget
