If you prefer to use the keyboard, select the text. For a superscript, hold down the command and shift keys, then press the plus sign. For a subscript, hold down the command key and press the ...

Once you've turned on subscript with the keyboard shortcut, you can then use the keypad to enter subscript numbers. Press "Ctrl-+" in Microsoft Word on a PC or a Mac to enter subscript mode.

Select the text, symbol, or number with superscript or subscript you want to remove. On the Home tab, click the launcher button on the bottom right of the Font group. A Font dialog box will appear ...

Microsoft has added the option to use superscript and subscript in OneNote for iPad. The functionality is currently in preview among Insiders and should make its way to everyone in August 2023.