Cfrgtkky

Suspecting that it's not installed I tried again:

sudo apt install gnome-tweak-tool



Reading package lists... Done

Building dependency tree       

Reading state information... Done

gnome-tweak-tool is already the newest version (3.28.1-1).

The following packages were automatically installed and are no longer required:

  app-install-data apt-xapian-index couchdb-common libnih-dbus1

  libqt4-designer libqt4-help libqt4-scripttools libqt4-svg libqt4-test

  libqtassistantclient4 python-apt python-aptdaemon

  python-aptdaemon.gtk3widgets python-attr python-automat python-blinker

  python-click python-colorama python-constantly python-cups python-debian

  python-defer python-dirspec python-httplib2 python-hyperlink

  python-incremental python-jwt python-oauthlib python-pam

  python-piston-mini-client python-pycurl python-qt4 python-qt4-dbus

  python-serial python-twisted-bin python-xapian python-xdg

  python-zope.interface python3-piston-mini-client python3-xapian

  software-center-aptdaemon-plugins

Use 'sudo apt autoremove' to remove them.

0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.

I also tried installing my computer with no difference. I still get:

gnome-tweak-tool: command not found

I'm on Ubuntu 18.04

How do I actually start gnome-tweak-tool?

In Ubuntu 18.04 aka Bionic Beaver the gnome-tweak-tool is a transitional package which is used to pull in a different package, in your case gnome-tweaks to make upgrades more smooth when a package name had to be renamed. For whatever reasons...

You can see this information when using apt-cache show gnome-tweak-tool. The Depends: line is the package that is pulled in.

So to run it, just enter gnome-tweaks or use dpkg -L gnome-tweaks to list the files that are shipped with that package.

The gnome-tweak-tools package provides the binary, gnome-tweaks. If you check out the package's details, either in the CLI or through Ubuntu Packages Website you can see this, where it shows the package provides gnome-tweaks.

You should be able to run gnome-tweaks, and the command will be found.

Using the package information, but also installing bash-completion, and using your TAB in the terminal, will help you figure these things out a bit faster. Here, you could have typed gnome-TABTAB, and gotten a list of available commands, showing gnome-tweaks.