[rspeer]

I tried to look up what U+2FA1D, the highest-numbered printable character, means in context.

It is a Traditional Chinese character. It's a variant of U+2F600, 𪘀, which is pronounced "pián". It apparently is used in zero words. It's in Unicode because it's listed in the 7th section of TCA-CNS 11643-1992, a Taiwanese computing standard.

Searching for it gives lots of sites that acknowledge that it's a character that exists and then provide no definition for it.

My guess: it occurred in someone's name at some point. Pretty strange that it ended up requiring a compatibility mapping, though, when nobody seems to use the character or the character it's mapped to!