How to type symbols, wherever you are typing

The shortcut depends less on the character than on the program. Alt+X is a Word feature and does nothing in Google Docs. Alt codes need a numeric keypad, which a laptop does not have and a phone never will. Excel would rather you used a formula. These pages say what each place actually requires, and which characters people ask for there.

Blank and invisible characters are their own problem: eight of them, and choosing the wrong one breaks a file rather than a name.

10 places, and the shortcut each one actually wants. For the character itself rather than the program, every character has its own page.