It looks like you are running XFCE instead of GNOME (the normal Ubuntu desktop). I’m not sure how that happened… but you an always just install another desktop.
For instance, you can try to make sure you have the ubuntu-desktop
or ubuntu-desktop-minimal
metapackage installed:
sudo apt install ubuntu-desktop-minimal
After that, the login manager should allow you to select the Ubuntu session rather than the XFCE one.
This is a great summary. Thanks!