If you want to remove the bar with the window names at the bottom, disable the Window List extension from the "Extensions" section of (GNOME) Tweaks or from this webpage: https://extensions.gnome.org/local/ (need to install one browser add-on/extension suggested by the page first).
Also there's a possibility that you have (unintentionally) logged into a "GNOME Classic" session which has "Window List" extension activated by default.
In that case reboot (or log out) and on the login screen, after entering your password click on the cogwheel (⚙️) next to the sign in button. It should show you different available sessions. Choose "Ubuntu" (or Ubuntu on Xorg) or "GNOME" (or GNOME on Xorg, but not GNOME Classic) session.