Comment 23 for bug 1838919

Installed packages don't matter if their content isn't in use. It does matter whether you run an X11 or a Wayland session.

To switch between both, log out to get to the login screen. There is a gears icon right above the password entry field, click on it. This should open a menu allowing to choose between "Ubuntu on Xorg" and "Ubuntu on Wayland". Having this choice done, log in, you'll be in the selected type of session.

Basically, all applications work in both session types, but there are a number of smaller visual distinctions. For example, Firefox draws its menu inside the window bar on Wayland, while it draws the menu under the window bar on X11. Also, on X11 there's a process "Xorg" running, while on Wayland there's a process "XWayland" (or similar).