The Alt numeric keyboard routine is using the position of the character in CP-1252 Windows encoding. It works only for character positions up to 256. Unicode accesses all characters in the font, for instance &uFBE4 position 5054, last character in SegoeUI.
Using Unicode guarantees it will be perfectly cross platform (as long as the glyph is in the target font).
That said, ° is a direct key on the French keyboard 