On Linux, press CTRL-SHIFT-U, unicode hex code, ENTER to type the unicode symbol. On Windows, hold ALT, press + (on numberic keypad), unicode hex code, release ALT key. This works for some apps. For others, try typing the hex code and then press ALT-x. You can also repeat to remove the unicode symbol.

https://en.wikipedia.org/wiki/List_of_Unicode_characters

°: B0

²: B2

Ω: 03A9