The keybinding to enter super-script text in gdocs is CTRL + ..

However, when pressing this on Ubuntu 22.04.1 LTS, and GNOME 42.2, it inserts an underlined e, which then locks the backspace key from working, but allows characters to be typed. Pressing ESC removes the underlined "e", and the text inserted after it, but pressing ENTER just removes the e.

Obviously with the way search engines process text input this is quite hard to search for and find an answer.