[klodolph]

The available space is closer to 2^20 (0-10FFFF, minus surrogate pairs, depending on whether you are talking about Unicode scalar values or code points).

[Someone]

There’s also Emoji modifiers (https://en.wikipedia.org/wiki/Miscellaneous_Symbols_and_Pict...) and regional indicators https://en.wikipedia.org/wiki/Regional_Indicator_Symbol that complicate determining the number of Unicode characters.