Ubuntu comes with a default terminal emulator, GNOME Terminal. But due to the limit of the underlying vte, many users don't want to use it. If you want to set a different program as default terminal, so that you can invoke it with Ctrl + Alt + T, here is how to do it.

Determine the desktop file of your terminal, by searching in /usr/share/applications/ or ~/.local/share/applications/. For example, kitty has one at ~/.local/share/applications/kitty.desktop, Ghostty has one at /usr/share/applications/com.mitchellh.ghostty.desktop.

Edit the ~/.config/xdg-terminals.list file (create it if it does not exist). Add the name of the desktop file at the top. For example, here is mine:

com.mitchellh.ghostty.desktop
org.gnome.Terminal.desktop

Before Ubuntu 25.04, there was another way, that is to set via update-alternatives --set x-terminal-emulator. But it is no longer respected by Ubuntu 25.04.